Such a true statement of fictional characters, too. Characters, like real people, should be complex. They should have flaws and contradictions and temptations. They shouldn't always be in a good mood or have perfect answers for every situation. They need to be confused sometimes. Torn. Scared. Overwhelmed.
In fact, the more real we can make our characters seem -- the more real-life traits we can give them -- the more invested readers will be in them. If we create layered characters, it will be more difficult for the readers to let them go when they turn that last page. For me, as a reader, that's the true test of a GOOD book - one I'm sad to leave when it's over (because of the characters).