At 20, Warren Buffett lost $2,000 on a gas station. Fifty years later, he told a classroom the real loss was $6 billion. Buffett had roughly $10,000 to his name. He put one fifth of everything he owned into half of a Sinclair filling station with a friend from the National Guard. The station failed. He lost the entire investment. On paper, the mistake cost $2,000. But Buffett measured mistakes differently. Every dollar he lost also surrendered every return that dollar could have compounded into. By 2001, he calculated the opportunity cost at $6 billion. Then he told the University of Georgia classroom that his largest mistakes were even harder to see. They were not bad investments. They were investments he understood, could have made, and did nothing about. He passed on Fannie Mae when it was inside his circle of competence and available for almost nothing. Buffett estimated that hesitation cost Berkshire at least another $5 billion. Neither loss appeared in an annual report. There is no red number for money you never earned. That is why Buffett proposed giving every investor a punch card with only twenty slots. Every investment made for the rest of your life would use one. No replacement card. You would stop buying companies mentioned at parties. You would stop chasing whatever made your neighbor rich last week. Every decision would have to survive the knowledge that nineteen opportunities remained. This is the same inversion behind Charlie Munger’s rules. Most investors study the money they lost. Buffett and Munger also measured the fortunes their decisions prevented from ever existing. A bad investment leaves evidence. The most expensive mistake of Buffett’s life left none. Which is more dangerous: the position that loses money, or the opportunity that never appears on your statement?