I think it is easy for singles (specifically women) to get bitter from a series of unsuccessful relationships.
Lately I have been thinking about the idea of a good person in the wrong position. I was thinking about it in the context of work and how in the wrong position, your positive qualities can be diminished. When in the right position, you are passionate and work hard because you really want to.
I think this spills over into relationships as well. I hate the whole 'all men suck' thing that single women sometimes say. I think it goes back to the wrong position and in this situation, wrong relationship. In the wrong relationship, the worst of you can be revealed, as opposed to the best (this I can personally attest to).
This idea has helped me when I have been 'scorned' in dating. I don't ever want to be bitter about relationships and hate men.
Just something to think about.