To completely eliminate the possibilities of ever going broke, losing players need a big enough bankroll to outlast their life expectancy. A professional poker player should realize that every dollar he wins will not be added to his bankroll. After all, he has to pay rent and buy groceries just like anyone else. Reducing one's bankroll converts capital into income - and the distinction is an important one. Change too much capital into income and you've eaten your seed corn.
Limit poker is like a job.
As long as you're a winning player, the more hours you put in, the more money you'll earn. Forget about money management. Forget about quitting when you're ahead or quitting once you've lost some predetermined amount of money. Chances are you'll win even more money. If you're losing, but haven't let your losses get the better of your emotions and you're still making good decisions at the table, there is absolutely no reason to quit.