The Statistician Who Drowned (in a River with Average Depth 3 Feet)

A statistician drowned crossing a river with an average depth of 3 feet. How? Parts of it were 12 feet deep. Averages hide the extremes. Your average customer spends $50—great! Except 90% spend $5 and 10% spend $500. Those are two completely different customers who need different strategies. But if you only look at the average, you optimize for nobody. Same in manufacturing: average defect rate of 2% sounds fine until you realize one production line is at 0.1% and another is at 15%. Averages smooth out the truth. They make you comfortable when you should be alarmed. They hide the gold (power users) and the disasters (broken processes).