the cheater

we all know the phrase "once a cheater, always a cheater". I know also that a lot of you will not agree that this is not always true. The men are the most famous for this title, However, basing on my friends, my guy friends are the loyal ones and my girlfriends are...should I say "the most experienced on this subject". So, I think the better phrase is, "What makes a cheater cheat?" What do you think?