Creating Interesting Characters

On DeepGenre, David Louis Edelman wrote an article on Building Character(s). In the comments section, Sherwood Smith said something I found very useful about creating interesting characters:

...A couple more possible additions to your list:

1) Character emotional range. If the character is always gloomy, always sarcastic, always with the wise-ass quip, or always nasty, even if he or she has all the motivation in the universe, that character is going to read one-dimensional because we all know we’re a bundle of (usually contradictory) emotional reactions. The hard-assed villain at a light or even tender moment, the hero being off-balance, the side-kick having the cool head, you get the idea, giving characters range helps because:

2) The perception of lack of dimension (I think) comes through readers’ expectations being fulfilled. If the reader can guess ahead of time how a character will react, even if there is every logical reason for the character to do or say that thing, then there’s no growth or guesswork. When the character takes the reader by surprise, I think it ups the ante, the possible interest.