r/Fitness does a weekly "Moronic Monday", a judgment-free thread where people can ask questions that they would ordinarily feel embarrassed for not knowing the answer to. I thought this seemed like a useful thing to have here - after all, the concepts discussed on LessWrong are probably at least a little harder to grasp than those of weightlifting. Plus, I have a few stupid questions of my own, so it doesn't seem unreasonable that other people might as well.
I don't think it's useful to think about constructing priors in the abstract. If you think about concrete examples, you see lots of cases where a reasonable prior is easy to find (eg coin-tossing, and the typical breast-cancer diagnostic test example). That must leave some concrete examples where good priors are hard to find. What are they?