@danluu @whitequark there's a pretty high degree of introspection and tracking required to even make that napkin calculation, though. Most people (and I'm including myself here for the most part) don't keep track of the time they spent on things, instead preferring to guess based on how they felt during the process, and how different answers might reflect on their own ability (to both themselves and external observers). What you don't look at closely can't hurt you.