From the Pen of David Morgan

Morgan’s Third Law of Writing:

The reasons for seemingly illogical behaviour should at least be hinted at in fiction, rather than relying on the audience to make post-hoc excuses for the writers.

 

Nicely said. From the Darths & Droids webcomic.

UPDATE: My wife reminds me that she has her own law of writing:

Mrs. Wright’s Second Law of Writing: The Reasonable Roleplayer Rule.

No character should adopt any plan if an average D&D player-character would have thought of cleverer one (such as taking along a super-soaker filled with Holy Water your interview with a vampire, or agreeing to a handshake rule with all party members when your enemy is Dr. Mirage the Illusionist).