A better prior is a worse (but not useless) prior plus some evidence.
You construct a usable prior by making damn sure that the truth has non-exponentially-tiny probability, such that with enough evidence, you will eventually arrive at the truth.
From the inside, the best prior you could construct is your current belief dynamic (ie. including how you learn).
From the outside, the best prior is the one that puts 100% probability on the truth.
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.