Money management is an essential part of any successful gambler's life. Before I made rules for my gambling behavior, it was too easy to convince myself that bad decisions were good ones. If I bet $10 on red in roulette and lost, I might think to raise my bet to $20 next, then $40 pending another loss. Betting red has nearly a 50/50 chance of winning, so under this betting scheme I am assured to win eventually. It is a good idea until you run of out money by risking $640 to win back your original $10.
Poker is different in that skill is a larger factor, but it is gambling just like roulette, or craps or the stock market. It is because poker is a game of skill that makes managing your money here far more important than with roulette—in which you are truly a victim of fate. Money management keeps you from going broke after a streak of bad luck.
Personally, I only have at risk 10% of my bankroll at any point in time. If my bankroll is $50 I only play $5 games until I have raised my stash to $100. From there I'll play $10 games, then $20 if my bankroll reaches $200. If I start to lose and fall back $150, I start playing cheaper games again. This can be hard to do. After all, I feel I am a good enough player to profit from $20 buy-ins, but I know if I stray from the rules I've set for myself I could end up at zero—or worse, in debt.
Chris "Jesus" Ferguson said he has turned $1 into $10,000 by a similar method; he actually played with only 5% of his bankroll. I know it would take us much longer than it took him to accomplish, but no goal is too high if you find a method that works for you and stay true to it.