The part that's really hit home with me is his advice for creating a three-dimensional character. He describes the three dimensions as:
- Outer affectations: Things people can see about the character from outside. For example, although he is a very well-respected and highly-paid brain surgeon, he drives a beat-up old 1970's sedan. The reader wonders why a guy who ought to have tons of cash drives an old junker. This may make the guy interesting but doesn't tell us much about him.
- Inner reasoning: Why does the character make some of the choices he does? Perhaps he drives the old sedan because he promised his late father he'd take care of his pride and joy. He can't part with the car because doing so would make him feel like he's abandoning that promise. This tells us a little about the guy, and may help us empathize with him.
- Behavior when the chips are down: We know the guy's old car is important to him, and we know why. But when he's in a situation where he has to destroy or abandon the car, or suffer something far worse, what will he do? Will he honor the promise at the risk of great personal injury or humiliation? Will he realize that life is more valuable than possessions? This tells us the guy's REAL character.
A truly three-dimensional character should show us all of these layers. They'll help readers identify and sympathize with them.