On March 27, 1977, two Boeing 747 passenger jets, KLM Flight 4805 and Pan Am Flight 1736, collided on the runway at Los Rodeos Airport on the Spanish island of Tenerife. Of the 644 people aboard the two 747s, 583 were killed and only 61 survived. This was the worst accident in aviation history. The massive investigation of and subsequent reports on the Tenerife airport disaster offer deep insight into what happened and what went wrong. As a result, aviation authorities and airlines worldwide changed procedures. But they are insufficient to explain why the KLM 747 collided with the Pan Am 747. Explaining the “why” of the disaster leads us to our great concern, bad decisions and what to do to avoid them when making a good decision is imperative for a mission-critical outcome.