Second, rich people tend to own unsexy businesses. A different study, by the statisticians Tian Luo and Philip B. Stark, examined which businesses were most likely to fold fastest. The kind most likely to go out of business most quickly is a record store. The average record store lasts just 2.5 years. (For comparison, the average dentist’s office lasts more than 19.5 years.) Other businesses that fold quickly include toy stores (3.25 years), clothing stores (3.75 years) and cosmetics stores (4.0 years).

There are, however, plenty of unsexy businesses from which a few people are getting rich. These include auto repair shops, gas stations and business equipment contractors.

The third important factor in gaining wealth is some way to avoid ruthless price competition, to build a local monopoly. The prevalence of owners of auto dealerships among the top 0.1 percent gives a clue to what it takes to get rich.