You cannot ever be inside someone elses head. You can never know exactly how they feel or what they are thinking.
Sometimes I have a problem remembering this, and I assume that I know how and why people are doing the things they do. Maybe this is because I really wish I did know. My freshmen year English teacher said that every single person as a reason behind everything they do. Nothing is done without a meaning in the person's head.
As convinced that you or I may be that we know he exact motivation behind an action, we can never be positive. Everyone needs to remember this. You wouldn't be happy if someone assumed they knew exactly how your mind worked, so why would you assume that you know their mind?
Sigh. This is just my general musing on humanity for the day. It's making me kind of sad.