prior probability

This is prior probability‘s second blog post … we wanted our first post to be something visual because lawyers and law professors often tend to express our ideas solely in words, but sometimes, ideas can be communicated more directly and more powerfully through visual images. For example, prior probability is currently writing a paper in which we try to visualize the problem of “probabilistic proof” in law. See http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2271870

So what idea or ideas does the picture below convey?