Always and never are two words you should always remember never to use. -Wendell JohnsonThis quotation reminds me that too often when we develop our characters we don't give them a mix of good and bad. We make the good characters very, very good and the villains horrid.
It makes it so much more interesting to read if you don't always portray your hero as good and never have him do anything bad. Likewise, I don't enjoy reading about a villain who is always bad and never good.
The mixture makes them believable. Life is not black and white. Mix in the gray and your characters will have more to talk about, worry about and will entertain us more realistically.