He sold 10% of Apple for 800 dollars

Apple was founded by three people. Steve Jobs, Steve Wozniak and Ronald Wayne, who drafted the first contract, drew the first logo and kept 10% of the company.

Twelve days later he sold it for 800 dollars. He had his reasons: partners were personally liable for the company's debts, and Wayne was the only one of the three with anything to lose. He signed, collected and left.

That 10%, held until today, would on paper be worth hundreds of billions of dollars. Wayne has said many times that he doesn't regret it: with the information available in 1976, he insists, he would make the same call.

That is opportunity cost: the real price of every choice is whatever you give up. It almost never shows up on the receipt. Wayne's is probably the most expensive invisible receipt in history.