This is not entirely true if you ask me because if you are familiar with casino games, you will realized that the probability of winning is not even up to 50%. What this mean is that you do not start off winning immediately but have to stay in the game and maybe get lucky on the process. So, it is not that gamblers are profitable for a start but refuse to stop due to greed. There will be exception to this sequence but I'm disputing your post primarily because you used the word "most" which is never correct.