...is also the most important thing, though that wasn't necessarily the case.
I find that over the last year or so, whenever a debate ceases to be about something in the world and becomes about pure semantics, a little bulb flashes up in my head - Standard Debate! "Yes, I know it's only tiny, but the question I'm asking is, is Pluto a planet?"
Followup to: The Most Important Thing You Learned
What's the most frequently useful thing you've learned on OB - not the most memorable or most valuable, but the thing you use most often? What influences your behavior, factors in more than one decision? Please give a concrete example if you can. This isn't limited to archetypally "mundane" activities: if your daily life involves difficult research or arguing with philosophers, go ahead and describe that too.