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I was reading this article called Behavioral Game Design, and it says:

...how do we make players maintain a high, consistent rate of activity? ... the answer is a variable ratio schedule, one where each response has a chance of producing a reward.

RPGs (I'm thinking of traditional JRPGs like Final Fantasy 1-6) don't do this when it comes to leveling up characters. You can always pause the game and look at how much XP you need to level up again. I haven't played WoW before, but I suspect it lets you know how much XP you need to level up, too. In WoW, there's plenty of examples of "variable ratio schedule" elsewhere in the game, so why not when it comes to XP you need to level up?

I suspect most professional game designers know the lessons in this article. So why is it typical for the XP you need for the next level to be known? They could design the game so that it's random, where you never know how many enemies you need to kill for that next level. So why don't they use this as an opportunity to have a "variable ratio schedule"?

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    \$\begingroup\$ As a sidenote: Some Pen&Paper systems, e.g. The Dark Eye, let you use your XP directly to improve your abilities. For example, a quest gives you 100 XP, which might be enough to increase your strength from 10 to 11, increase your dagger skill from 6 to 8 or unlock a level 1 spell. That avoids the whole "X XP to level up" thing and provides constant progression. \$\endgroup\$ – Morfildur Jan 28 at 7:36
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    \$\begingroup\$ @Morfildur comparable with souls in the Dark Souls games \$\endgroup\$ – JAD Jan 28 at 7:39
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    \$\begingroup\$ Your referenced quote doesn't really counter your point. For example "producing a reward" can mean getting a somewhat randomized XP value; but that doesn't mean you can't know how much XP you need for the next level. The variable ratio can come from either the (uncontrollable) input or the (unknown) goal, but the effect remains the same. \$\endgroup\$ – Flater Jan 28 at 7:44
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    \$\begingroup\$ I’d just like to point out that there are games that randomise the XP system, just not the amount you need for the next level. Instead they randomise how much XP you gain per action (slightly more, slightly less). Of course, since you need to do these actions many times it doesn’t really influence anything – the result is the same as gaining the average each time. \$\endgroup\$ – 11684 Jan 28 at 9:20
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    \$\begingroup\$ Imagine a korean style RPG, for leveling from [max level -1] to [max level] you need about 20-50 hour grind. Now you hide the XP, and randomise the Xp from mob. the play have to experience 20+ hour grind in the dark. With no positive return, no information. After few, every time you will give the player an XP < The maximum Xp in the range, He will believe that you are slowing him down, After 10k kill a 1% behind the top value is a big loose. Without the XP% progression. \$\endgroup\$ – Drag and Drop Jan 28 at 12:40
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It's common for games to have multiple overlapping loops of gameplay and reward, hitting different frequencies and motivation types, so that we don't have all our eggs in one basket, motivationally speaking. This helps the game appeal to more players, and more consistently appeal to any one player, since every player is a multifaceted human being with a variety of interests & needs.

RPGs typically scratch the "variable ratio" itch with combat and loot drops. You have a random chance of encountering this mob or that mob, a random degree of success on attacks and dodges, and a random reward on completion. Unknown rewards in chests and breakables found as you progress through the world function similarly.

This forms a very high-frequency loop every few minutes of gameplay, making it well suited to produce a feeling of "just one more fight!" - a good loot roll could be just around the corner, and it only takes a few minutes more to try another time.

XP and leveling progression serve a different niche, on a longer term - ensuring the player can see they're making measurable progress and growth over hours of gameplay, or from one game session to the next. Even if I get a terrible sequence of loot rolls and am nowhere closer to crafting that shiny new item, hey, at least I'm 1000 XP closer to my next level, so I'm still being productive and haven't wasted my time!

Because of the longer timescale of leveling, a random chance isn't quite so motivating here. I don't want to sink another hour of play just for a chance I might level up. For an investment that large, a player will typically want some predictability. Even if I don't manage to hit level n+1 today, knowing I'm just 500 XP away makes me eager to come back and finish the level tomorrow, opening up a new long-term goal of hitting n+2...

So, it's not that these games forego variable ratio rewards, they're just choosy about where they deploy them.

Player expectations are a factor here too - players have a lot of experience with random loot drops and predictable XP progression at this point, so sticking to this convention helps the players feel comfortable, and learn the systems efficiently. Suddenly making level progression randomized risks alienating players, so it's often safer to place those variable ratios elsewhere in the game design.

This expectation might be a factor in why RPGs that have decided to use variable ratio rewards as their long term progression — eg. Destiny and other games with high-end leveling based on gear score — have chosen to do so via the loot system, to better match where players are used to seeing this type of randomness. They could as easily have given out a "level token" randomly, but by attaching leveling to the quality of gear that drops, they piggyback on a familiar gameplay pattern of loot grinding, and also give more interest to the "failed" rolls. (ie. Gear that doesn't increase your net level might still be useful to sell, use in crafting, or have some other value like a special ability useful in some circumstances, or a desirable visual appearance)

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    \$\begingroup\$ This is a great response, but there's something I still don't understand: Why not make everything variable ratio rewards. The article says most SPECIES find it irresistible (not just most humans). It seems to contradict what you said here: "since every player is a multifaceted human being with a variety of interests & needs." \$\endgroup\$ – Daniel Kaplan Jan 28 at 5:16
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    \$\begingroup\$ @DanielKaplan It's a matter of looking at the reality of the industry as opposed to taking someone's theory as ultimate truth. Industry shows that if you're going to sit in front of a screen for a reasonably long time, you want some guarantee that your expectations of advancement will be fulfilled. Demands on people's time are increasingly manifold - this is also why simpler games have become very common. This answer is spot on. \$\endgroup\$ – Engineer Jan 28 at 6:50
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    \$\begingroup\$ @DanielKaplan I don't play slot machines. There is no draw for me - I might win or I might lose - there is no middle state. Yet slot machines are exceptionally popular else they wouldn't be around. The fact that I don't like them doesn't mean somebody else shouldn't, either. At the same time, I really like playing games like Diablo or Path of Exile or Warframe - there is a high amount of chance in drops that is not unlike a slot machine but you also have other kinds of guaranteed progress that draw me in. But for others, those might take too much time. Both are correct. \$\endgroup\$ – VLAZ Jan 28 at 7:28
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    \$\begingroup\$ @DanielKaplan there's no contradiction here. Yes, a variable ratio reward is reliably compelling. No, it's not the only way to motivate a player, nor the only one worth using. Beware of any model of human behaviour that tries to distill it down to just one rule - we all know people are more complicated than that. You can get a human engaged in variable ratio activities like slot machines, but usually not for a very long time - there's other stuff we care about doing too! By diversifying the motivational strategies we use, we make the game more robust to fatigue of any one motivation loop. \$\endgroup\$ – DMGregory Jan 28 at 18:28
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    \$\begingroup\$ @DanielKaplan Variable ratio reward mechanics scratch the itch for people to want to risk and gamble. Not all people have that itch. (In fact, I would wager that most people will repeatedly come back to a game because of predictable and quantifiable long-term progression, not because of random-chance rewards.) Of course, most widely popular games utilize both mechanics, both on their own and in conjunction with each other. (e.g. Final Fantasy has a level progression system but also has monster drops, incentivizing both long-term leveling goals and random spikes of "oh cool" moments.) \$\endgroup\$ – Abion47 Jan 29 at 0:30
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It's a matter of motivating the player.

  • The player has an achievable goal to work towards
  • The player sees how far away from the goal they are
  • The player sees how playing the game visibly progresses them towards the goal

Variable ratio rewards can also be a great motivator, but so is an "honest pay for honest work" game mechanic where the reward after each action is guaranteed. The player never feels like doing something was pointless, because there is always at least a minimum reward in form of experience points.

Many MMORPGs recognized this and made the levelup progress bars much more accessible than classical single player RPGs. They are often very prominent, always visible UI elements. I have seen MMORPGs which made the EXP progress bar span across the whole width of the screen. Some even make it a two-tiered bar with one bar showing the progression between 0% and 100% and a smaller bar below showing the progress to the next full percent. That way players can still see visible progress when they get into the lategame phase where it takes several days to level up.

Using experience and gold as a reliable reward and item drops as a variable reward has proven to be a practicable and effective combination. So it basically became a standard convention of the RPG genre. There is of course no reason why you shouldn't try to do it the other way around in your game. I could see it work quite well. But keep in mind that you are in experimental territory here.

In more "skinnerboxy" games you see a lot of such numerical progression systems. Progress to next level, progress to levelup individual skills, progress to completion of quest, etc.. The player should always find something to work towards.

One secret of addicting game design is to layer many different reward systems which stimulate the player's reward neurons in as many different ways as possible:

  • Short-term, mid-term and long-term rewards
  • Constant, slightly variable and you-just-won-the-lottery variable rewards.
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Think about what would happen if level up happened randomly. You have a party of three players. At the beginning, all are the same level (for simplicity, 1). After playing around one levels and two don't. Not a huge deal normally. Since the one leveled, the others will level next and catch up. But under your system, the one who just leveled may level again before the others do. Over time, you end up with one person who was really unlucky and is level 5. Another is level 7. And the lucky one is level 11.

How does the system balance a party with a level 5 and a level 11? The level 5 player will die if the encounter is set up for a level 11, and the level 11 will be totally bored if the encounter is set up for level 5. And if they compromise and set up for level 8, they have both problems at the same time. The level 5 is constantly dying while the level 11 is constantly bored.

Now, perhaps you play solo. So this doesn't matter to you. But if the game is designed to include team play, it has to handle this issue. And they can't really have different behavior for this in solo versus team, as the same characters can participate in both. Even if your game is solo only, players will expect it to work like this.

Another problem is when the luck is going against you. You're stuck at level 5. You can't advance because you're waiting to level. You get tired of the game and quit, because it's a constant grindfest as you wait to level.

A third problem is when you level early. There's a certain amount of level 5 content. But you leveled and can do level 6 content. Do you stay and do the now easy level 5 content? Or do you switch to level 6 content? If you switch, you're essentially skipping part of the game. Your enjoyment is reduced because you didn't get the full content. And if you do the level 5 content anyway, you get bored as the encounters are not challenging to a level 6.

It can get worse. While you're doing the extra level 5 content, you may level again. Now you're a level 7 doing level 5 content.

This problem is reduced with loot, as it doesn't progress the same. You find a good sword. How lucky. Then you find a great sword. But having the good sword doesn't make the great sword any more powerful. Having a level up event on top of another level up event is more powerful than a single event. So the second amplifies the first. But with the swords, each drop is isolated.

All this isn't to say that you can't have random variation in the experience rewards. But with team play, you want all the members of the team to get the same experience result. And in solo, you have to find ways to match the difficulty to the player's capability. If you have both, then you need to be consistent between them.

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  • \$\begingroup\$ 'Bad luck' will tend to average out given enough time, but your other points about content and difficulty are very valid. \$\endgroup\$ – DaveMongoose Jan 30 at 17:05
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The short answer: psychology.

The long answer:

We humans are driven by the expectation of a reward, just like a dog. Knowing how much experience you have reached and how much is still needed for reaching the next level gives you a nice feedback that what you do is good or bad for evolving your character.

Edit: also, not knowing how long it will take for levelling up is like downloading a big file without a progress bar. It may take the same 10 minutes, but without a progress bar it will feel like 10 hours

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    \$\begingroup\$ I like the progress bar analogy. Fits very well with the core of the question, which is stated in the title. "Why do RPGs let you know how much XP you need to level up?" \$\endgroup\$ – Tim Holt Jan 28 at 22:52
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    \$\begingroup\$ @TimHolt - Because it can't be random - Brythan's answer, so you either tell us or we have to do the math or look it up. I've seen status bars that are full but not done yet : I'm looking at total file size (xp till) and Mbps (xp per encounter). \$\endgroup\$ – Mazura Jan 29 at 14:42
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There is actually a quite interesting GDC talk that has been given on this topic by someone who worked on the reward structures for large sections of World of Warcraft and Diablo 3:

https://www.youtube.com/watch?v=urijgWXLYck

He talked at length about how players experience randomized versus deterministic rewards and how both reward types work together to provide a player with a sense of progression while also encouraging them to continue playing. I also recommend a related video from someone who played World of Warcraft for a long time, a video that gives his own comments on the video and clarifies a number of things from the perspective of the player:

https://www.youtube.com/watch?v=OjQAnJYyXf4&t=0s

I recommend watching both videos if you have time, because they provide a good overview of the challenges with reward structures and how he solved deterministic versus random rewards.

He found that in order to keep players playing, they need to feel like they improved meaningfully every time they played, even if they only played a short while and only got a small reward. That's the role that EXP delivers: you can play a short period and still feel like you did something worthwhile with your time. He also found that if everything was deterministic, the player dynamic would change and they would view the game more and more as a really grindy system that was very predictable in pacing and felt like a deliberate slowdown of the game. This was especially noticeable during Icecrown Citadel and Firelands, when Emblems of Frost and Dragonwrath respectively changed a large and impactful part of progression to a mostly deterministic path, where you could predict when you'd get the next step in your gearing process months in advance and guilds planned around them.

He had exactly the reverse problem in Diablo 3: the loot players got was too random and often not usable for their class, so players would go days or weeks without any upgrades because the few legendaries they'd get were meant for one of the other 4 classes. The result is that players would stop playing the game for their OWN loot and instead played to get as much loot as possible to sell on the ingame Auction House so they could then buy their own gear with the proceedings. It turned the game entirely deterministic and players were quitting the game in droves because the core part of the game felt unrewarding. They additionally also had the problem where their intended max level deterministic reward, Paragon levels, would eventually cap out and players would no longer see reason to continue playing for them.

That problem was solved through removing the AH, redesigning Paragon so there was no level cap, and rebalancing player loot drop rates so they would get far more legendary rewards and far more rewards that were suited for their class. They then found that their loot had pretty much become deterministic, which they fixed by adding Ancient items, which essentially were Legendary items with more stats on them. They also added a way to more or less target specific items, but without losing the random chances.

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TL;DR

  • People are impatient.
  • More randomness tends to make games more difficult.

As you have pointed out, it's been scientifically proven that many species find variable ratio setups 'irresistible'. This is because they appeal to a very primitive part of the brain, and assuming that the individual judges risk/reward ratios correctly, it's actually a really important survival trait. Because it's such a low-level response, it's really hard for most people to not follow up on it, and therefore it does indeed make a good draw for a lot of players.

The problem is, this impacts behavior in ways people might not expect. People don't like to wait for results to be visible, they want them now, which in turn means that for many people, no visible progress towards a reward equates to zero progress towards said reward, which then means that most (sane) people will stop trying to get that reward after a while. This is actually the same reason that a 'clicker' or whistle is used when training animals, it helps fill-in the space between the desired action and the tangible reward, making it easier for the animal to equate the action and the reward mentally.

As a result of this, people tend to get irritated when they make no visible progress after spending multiple hours working on something (not just in games, but also in real life). The exact point at which this starts to become an issue varies from person to person, so most games err on the conservative side here and give you easy access to exact information about how far you've progressed.

Some people go even further than this though, and want to know exactly what they need to do to to achieve something, and as a result you can find information on exact amounts of XP you get from any given action in a number of the more populate RPG's out there with a simple search of the internet.


All that psychology is useful info for explaining this, but there's an even more important, and much simpler, line of reasoning that explains it, leveling is one area where more randomness makes a game really hard, and if you're not going to make it random, you might as well just show players the numbers because they're going to figure them out themselves through experimentation anyway.

Imagine trying to level on a bell curve. You have to get some minimum amount of experience to possibly get the next level, are guaranteed to get it after getting some higher amount of experience, and most people level about halfway between those two numbers. This has all kinds of issues:

  • In a single-player RPG, it makes the game much less consistent. This can technically increase replay value for veteran players, but it can make the game hellishly difficult on a person's first play-through (or insanely easy, in which case they may not end up liking the game as much either).
  • In a drop-in co-op RPG (like Borderlands), it makes it very difficult for people to actually work together as a team. Part of the reason such games work at all is that they provide reasonable guarantees that a group of people who start the game at the same time and only play together will have roughly equal power levels. Without that guarantee, the whole format falls apart (because anybody who gets lucky a couple of times will constantly steal the spotlight).
  • In an MMORPG, it just makes things miserable in general. Imagine playing WoW or Warframe but not knowing when you'll be high enough level to join your clan/guild on their next big raid. It's just as bad for sensible clan/guild leaders, because they can't realistically organize long-term coherent groups of people who are about the same level to progress together.
  • In any type of RPG, it makes coherent story progression nearly impossible (oh, I finished this series of story quests, but I'm not quite high enough level yet to be able to even attempt the next set of story quests, guess I have to go grind enemies from the last quest for a couple of days instead of getting further in the story).

It also, somewhat ironically, would make the developers life much more difficult. This approach would require a lot of complexity in the code that ahndles leveling, and complex code is more difficult to maintain, more difficult to debug, and more likely to have bugs. Even systems which have you send XP directly on power ups instead of leveling are simper than this.

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    \$\begingroup\$ Good answer. Something you didn't say directly: When there's a lot of time before your next level and you can't see your progress, humans can't tell if it's random or if the reward has stopped, and they'll probably assume the latter. The article mentions that's very frustrating. \$\endgroup\$ – Daniel Kaplan Jan 30 at 0:27

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