Nice men are single because..

The claim that niceness causes singledom skips the real variable: passive niceness with no standards reads as low interest. What's the line between being kind and being a doormat?

Learned helplessness

The reality of the question is so much more disturbing. Nice guys are taken for granted and milked dry. It's easy to manipulate a nice guy, when you shouldn't want to. Don't change him, he's already nice. He provides and is kind. If you want a bad boy, go get him before you breal a good soul. Don't change him into something he's not.

Don't confuse nice with wimpy. Women are OK with nice, they don't typically like wimpy.

att vara snäll är det viktigaste fattar inte kvinnor

who is the woman in the video? Source?