Since no one is around to see or hear a tree falling, one must just assume since trees do sometimes fall- that it could certainly have happened. So say you are desperate for firewood. The only place to get it is in the forest, so you are hoping a tree fell sometime. You're freezing your butt off. You don't KNOW if there's a fallen tree, but what if there IS? There is no sure way to know until you get to the forest to look.