Some people stop when they have made profit although it is actually quite rare for someone to quit while he is ahead. The most important thing is not to stop but rather to be aware of your own bankroll, you dont want to lose everything in one game and move on to be a beggar for the rest of your life for sure
Even if you are going to stop and aware of your own bankroll if you don't have control for yourself, you can still have a lot of lose. Because that is basically a normal attitude of gambler, he keeps on gambling again and again because he thinks that his luck will lasts for a longer time but what is happening is worse than he isn't expecting.