What about the Other Characters?

Most readers, I suspect, assume that a story’s perceiving character will come from the writer’s own psyche, at least to some degree. Not that authors must commit murder to write from the perspective of a murderer, but to do so we must be able to get in touch with the part of ourselves that might, given the right circumstances, be capable of such an act.

What about the side characters, though, the ones the writer doesn’t climb inside of? If characters are only observed, not inhabited on the pag...