The Bullet Hole Misconception is an infamous real-world “balancing” error where Allied Command in World War II kept losing bombers to anti-aircraft fire, so they decided to make improvements to plane armor. Officers studied returning bombers to see where they were being hit the most.
Essentially, they counted the bullet holes and decided to reinforce the three areas (tail, wings, fuel tank) where they saw the most damage. On the surface, that seems like it makes sense but the issue is that they were only studying returning bombers, i.e. the ones who were able to survive long enough to make it back to base. The three areas where Command wanted to focus protection were, ironically, already some of the safest on the bomber, as those spots could absorb a good deal of damage and the craft could keep flying.
The actual major failure points on the plane were the places that had the fewest holes (cockpit/engine) since the bombers being shot there were the ones who weren’t making it back to base.