The best way to control greed in gambling is to set a deadline to keep most of the revenue earned. I mean we need an alarm to set a time limit so whatever happens we have to retreat calmly. It seems unreasonable, but so far effective to save many wins.
Setting alarm and controlling yourself is not a possibility 
People who gamble are greedy and that is the fact,they hope that they could make some easy money if you are lucky and so is the reason you could see many people coming into gambling sites,if you are playing with skill based gambling then you could make money ,the rest are just too much risky .