Robert A. Heinlein on writing

From Cory Doctorow’s “How Heinlein plotted” (Boing Boing: 22 July 2010):

My notion of a story is an interesting situation in which a human being has to cope with a problem, does so, and thereby changed his personality, character, or evaluations in some measure because the coping has forced him to revise his thinking. How he copes with it, I can’t plot in advance because that depends on his character, and I don’t know what his character is until I get acquainted with him.