I think people are not successful in poker for the following reason: there is a life behind poker. Some of us need to work, to study, among other things, and you need a source of money to survive.
One thing is very different if you already have money, an economic stability that allows you to focus on poker and nothing else.
Equally for me, you really have to be passionate about poker so that you can devote study time to the game, to the strategies, and to resign other things through the schedules