Yes, it is the greed which make us loss in gambling. I remember a few months ago, i played dice and was winning together few consecutive wins. I was playing with a strategy and keep on investing slowly. Just than greed came in and i invested all my profit at once and lost that on a single dice game.
Anyways that was part of the game as there are many good moments in gambling too. It is a game where you will enjoy both the moods, Good and Bad, depending on the luck.