I'd go with: Probability exists in your mind, not the world, but there still is an "objective" way to calculate it.
I like it. In the spirit of iterative improvement, how about this:
Probabilities are subjective, but the information they represent is not. Use all available information on pain of paradox.
People want to tell everything instead of telling the best 15 words. They want to learn everything instead of the best 15 words. In this thread, instead post the best 15-words from a book you've read recently (or anything else). It has to stand on its own. It's not a summary, the whole value needs to be contained in those words.
I'll start in the comments below.
(Voted by the Schelling study group as the best exercise of the meeting.)