You need to be in control of yourself. This means calculating every single decision you do. If you manage to subtract the feelings from the decisions you make you will be able to null the greed and generate profits.
I'd agree that self-control is very important when it comes to gambling but trying to completely remove any feelings can be extremely dangerous as well! If you have no feelings it can help you generate profits but it can also make you lose any sense of reality which means you'd go down in a horrible spiral where you just keep on losing..