The dark figure of supply chain detection
During World War II, Abraham Wald was asked where to add armor to bomber planes. The military's instinct was to study the planes that came back and reinforce wherever the bullet holes were clustered. Wald said to do the opposite. The planes in front of him had already survived hits to those spots. That's exactly why he could study them. The planes that took hits to the engine or the cockpit never made it back to be studied at all.