I agree. Bankroll management is a very important part of being a great gambler, any veteran gambler would know that you do not go all in right away and make mistakes, you need to make sure that you are doing something decent with the amounts and could go on for a while before you run out of money. That's not a common thing done by people all that much, but I agree that it is going to be something special when you do and you could earn more money that way.
This could be done by studying and learning how to do bankroll management. If you like reading there are articles, or if you like watching then there are youtube videos about it that will teach you how to be a better gambler.
Yeah, if a player doesn't worry about bankroll management and doesn't control his emotions, the chance of winning will be close to zero in the long run. It seems to me that the optimal bankroll for slot games should be 500 or even 1000 times more than the initial bet per one spin. In other words, the principle is the same as in poker, except that the dispersion in slots is clearly many times greater than in poker.