Making your characters ignore themselves

Someone wrote me a note asking me to expand on something I said at one of the Astronomicon panels, and it made sense to post the quickie response here.

If you get a chance, I'm interested in a summary of your ideas on writing character and staying in character. You talked about liking to write a character that has inner resources s/he doesn't know s/he has that s/he is able to access later in the story. How do you set that up for the reader (while keeping the character in the dark) and make the act, when it comes, seem "in character" when the person has been shown as weak and perceives his/her self as weak?

The first thing that pops to mind about how to make a character reveal something new that still seems in character is: Make the character ignore that trait on purpose. If Jane is faced with the choice of throwing Grandma off a roof to save humanity, make her refuse to consider the Grandma question altogether. Make her fight to save humanity every other way, but let her avoid considering the Grandma issue every time it ought to come up. I've found I can make my characters more realistic by making them not say things. After a while, I think, the reader understands that Jane really is considering tossing Grandma, but hates herself for even thinking it. I think that helps make the conflict something so deep that the character herself isn't even fully aware of it. When you hit the climax that forces Jane to make her choice and she turns around and looks at Grandma for the first time, the reader yells, "Oh shit!"

So maybe the concise way of saying the above, is: One way to reveal a new side of a character is to make the character suppress that side (consciously or unconsciously), and the story forces the character to dig deep and re-evaluate that decision. The result is an about-face that was really there all along, but was brought out by the travails of the story.