At breakfast yesterday my granddaughter asked me to teach her about investments and how to handle money. This is an excellent question for anyone, especially a new college graduate headed to medical school.

I thought of Warren Buffet, who is the most successful investor of the twentieth century. How successful? According to Wikipedia, in 2008 (at age seventy-eight), “Buffett became the richest person in the world, with a total net worth estimated at $62billion.”

How did he do it? The answer is...