That's not the joke. The point is that the sun exploding is extremely rare, so you can essentially conclude that the trial is a false positive. If you just look

That's not the joke. The point is that the sun exploding is extremely rare, so you can essentially conclude that the trial is a false positive. If you just look at the p-value you ignore p(B| not A) (false positive), and conclude that the sun exploded (no actual statistician would make that claim in this example, but they sure do in more subtle situations).