Named after Robert McNamara, the U.S. Secretary of Defense (1961-1968), who believed truth could only be found in data and statistical rigor. The fallacy refers to his approach of taking enemy body count as the measure of success in the Vietnam War. Obsessing over it meant that other relevant insights like the shifting mood of the U.S. public and the feelings of the Vietnamese people were largely ignored. When analyzing complex phenomena, we’re often forced to use a metric as proxy for success. However, dogmatically optimizing for this number and ignoring all other information is risky.