Perfect imbalance relies on players shifting their strategies (collectively forming the meta of the game) in order to neutralize strategic advantages others might use against them.
That means we have two main ingredients:
- A community of players competing against one another
- Intransitive mechanics to counter other players' choices
Intransitive mechanics are named in reference to the Transitive Property in math, which says that if we know:
then for a transitive relation we can safely conclude that
A > C.
For a transitive rule and a finite set of options, there's always one that's not less than any other. If we think of our relation as being one of gameplay advantage, that means one option isn't strictly weak against any other option, though it might be equally advantageous as several others.
The risk here is that it's fragile - if we don't get that equality of advantage exact, then we end up with one option that's strictly better than everything else, and ones that are strictly worse. Nobody wants to play a worse option, so our game can become one-note as everyone piles up on the dominant options.
Intransitive or non-transitive rules break this. The most familiar example is probably Rock Paper Scissors, where:
Rock ---defeats--> Scissors
Scissors ---defeats--> Paper
Paper ---defeats--> Rock (the opposite of what a transitive rule would say, given the two rules above)
Now there's no way to put these into a strict order of better & worse - there's always a wrap-around point somewhere, some way to "beat the best." This makes balancing these types of mechanics much easier than in the transitive case, because we're not relying on exact parity of numeric relationships to keep two options balanced - instead it's baked into the cyclic structure of advantages.
In games you'll often see this expressed as counter relationships. A sniper character is weak against a fast/evasive character who can close the distance and take them on at close range, but that character will often be lightly armored and weak against a heavily-armored bruiser archetype, who might in turn be weak to being sniped from afar...
If a group of players is dominating by using one of these strategies, say the sniper, then other players can notice this and counter by deploying more fast/evasive characters, dethroning the snipers or forcing them to switch strategies. This keeps the strategic landscape dynamic, fighting the tendency to settle on one optimal strategy or tactic.
This works even when one of these characters/options is, by some definition, strictly more powerful. I recommend reading In Schreiber's Game Balance Concepts blog for the full details & math treatment on why. There he shows that even if we play a version of Rock Paper Scissors where rock wins count double (making it, at first glance, twice as advantageous to play), there's still a way for players to balance their strategic choices that keeps the game fair and interesting overall, without the game collapsing to always playing a particular option.
It doesn't always need to be exactly 3 options, or all in a single loop. Your move / unit / character / build / strategy relationships can be a spaghetti fractal of little loops inside bigger loops. As long as no one option (or group of options) is strictly dominated by all other options, nor strictly dominates all other options, then a sufficiently large & motivated player community will tend to seek out a ratio of choosing these strategies that overall roughly neutralizes individual advantage in the context of the current meta - something called a Mixed Strategy Nash Equilibrium if you want to get into the game theory of it. :)
Just beware that we can't rely wholly on this self-balancing feature of player communities to absolve us of all design responsibilities. Every strategic choice I need to make as a player just to counter the dominant strategies in the current meta is one less choice I have available to express my own play style and preferences - it's a choice that's effectively already made for me, constraining my play space. A little shifting of the strategic tides as the meta evolves can keep the game fresh over time, but when most of my choices are dedicated to fighting against the same lopsided design then I'm likely to be having less fun, and go look elsewhere for my challenge. So we still need careful balance, even when we allow it to be imperfect.