People who do stupid things to protect people important to themselves! People who are more than what they appear. People who seem to have another side of them (whether they recognize it's presence or not) and what it'd take for that to come out. People who are so ordinary in every sense of the word, and what happens when they are faced with a life-changing something, whether it's an event or situation or recognition of ______. People that start off one way and then change due to outside influences; what sort of influences and who and how these interactions affect the original "subject." What people would do for various...others/things.

This is what he's interested in, because humans are so multi-faceted and so changeable and emotional.