Why do some people realize that they can't rely on others for help, and how do they cope with that realization?

What's the best way to start a conversation about money with your partner when you're afraid it will cause a fight?
Do you have any tales about dealing with troublemakers where they didn't realize who they were dealing with until it was too late? How did it resolve?
Is it worth trying to maintain a relationship with a neighbor after they've done something that made you furious, or is it better to cut ties?