Personally I have my limits for the number of bets I play within a time frame. After 3 bets, I most likely back off even if I'm winning or losing. You are right when you mentioned that people get greedy and keep Betting when they win bets, making them lose at the end most times. Let's remove greed from the picture and know our limits.
Say it to those greedy stupid gamblers out there 
. They don't know what are they limits and they will just gamble and gamble and they will only stop if they have no money anymore. I also have limits when I'm gambling. Around 4-5 bets is enough for me and I only spend a small amount on it. I don't want to get addicted into gambling.Its easy to say those greedy gamblers, but it is hard that they understand it, because they have cross the limitations in gambling and they can't come and stop in limited manners, because they become greedy and have addiction of gambling.
Therefore, as a gambler in any gambling site we need to set goal or target for every time we are going to play.
Like if you want to play in dice games, once you see that your earning average is 3 to 5% you'll need to stop from there
then continue it on the next time you will play again. Because you are right we shouldn't be greed at all times.