Hmmm. What are the constraints on universal possibility, though? My understanding is that it's possible (albeit staggeringly unlikely) for any possible structure, including living beings, to spontaneously form via quantum fluctuation, and given infinite time and space every possible structure will spontaneously generate. If the many-worlds theory is true, then there's a universe where you were just crushed by a hippo that randomly materialized above your head. The odds of any given person tripping (possibly on a spontaneously-generated rock) and breaking his ankle on the day he would have been killed by a mortar shell seem pretty high, relative to that.