Here is a quote from a recent “kick” from David Farland that I found interesting.
“…In storytelling, the heart of a story lies in a character’s ability to change, to break from old patterns and find a successful course in life. A character who is incapable of change is almost always the villain–someone who is doomed to be destroyed because of insufficient wit or grit. ”
So if you want to write real characters, round instead of flat characters, characters that readers want to read about, make sure the characters change, evolve, or grow in some way. This is especially true of your main characters.