Cross sections for hadron colliders are calculated using perturbation theory. Since some or all of the particles involved carry strong interactions and the strong interactions are strong, it seems counterintuitive to use an expansion based on the smallness of the strong coupling. The explanation is that the strong coupling is small for physics at short distance scales, and we use perturbation theory only for the short distance part of the cross section. We thus rely on a theorem that allows us to factor the short distance parts from the long distance parts. I will review why we think this theorem is right while pointing out features lacking in its (so-called) proof.