somebody can probably find the real story better than I can. Back in World War 2, the B29 Bomber would go out on long flights but not all of them returned. Of the ones that returned, they saw the hauls were full of bullet holes, so they kept adding armor to the haul and kept losing planes. By focusing on the planes that were not coming back, it turned out the problem was holes in wings - planes were surviving the holes in hauls.