Meeting the cast

How well does a writer need to know her characters?

There seem to be two sets of conventional wisdom about this. One holds that writing characters is rather like method acting - the writer has to become the character, so as to know them from the inside. The other is more mechanical, and is typified by "character sheets" - pages-long lists of questions about each characters' physical and mental attributes and backstory.

Each of these methods works sometimes, for some writers, and doesn't work...