Success is defined as your equity in your studio is greater than the amount which you could have earned working for someone else's studio.
By and large, it is the same as any industry. An individual that has much technical knowledge in a field is able to make very smart technical decisions because they have much experience doing it. At the same time, they lack experience making smart business decisions because they generally lack experience in business management.
Making smart business decisions affects success way way more than making smart technical decisions.
The oversight or common mistake is to not employ an experienced business manager early on in the enterprise or somehow mitigate this shortcoming within the enterprise.
The moral: Find a good business manager and pay them more than anybody else in the enterprise. Sounds counter intuitive but the better manager you have, the sooner your enterprise hits critical mass where your studio achieves success.