Having (and keeping) Standards
It is common knowledge that many men will sleep with any woman willing to have sex with them. When a man is just beginning to have success with women, such a mentality is somewhat understandable. Somewhat. Past a certain point, though, having sex with sub-par women can have a negative effect on your game, because you subconsciously believe that is the best you can do.
Also, If you talk to the average guy, he drools over very attractive women, putting them on pedestals. I'm sure we've all read one of Maxims' "Hottest Women of the Year" type articles, where they just fawn over these women.
While there is nothing wrong with stating how attractive a woman is, many guys take it too far and begin to supplicate. Part of having standards means respecting yourself enough to know that no person is superior to you simply because they are beautiful.