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.
I had already been a Bayesian and fan of Kahneman-Tversky for 15 years before I started reading OB. So I didn't learn the basics there.
Given that, I'd have to say the most important thing I learned was to exercise unflagging discipline when thinking about values. For me, this means (a) remember to keep track of terminal versus instrumental values in any problem framing and (b) realize that most people's terminal personal values are complex and != "maximize pleasure".