most of the time greed starts to take over people's heads and they stop knowing themselves, and with that the disaster becomes bigger, gambling involves money and nobody likes to lose money, and you need to have a very mentality strong to be able to not get carried away by greed and addiction
Greed comes when people lose control, that's "full greed" and that is not good for gambling since you will be taking very high risk with high greed. In order to minimize the risk, you need to put yourself in control all the time, no one can win with greed their mind as they are not any more objective with their strategy, it's their emotion that would work hard rather than their mind.