Not everyone is an entrepreneur. Still, everyone should try—if only once—to start a business. After all, it is small and medium enterprises that are the key to job creation. There is also something uniquely educational about sitting at the desk where the buck stops, in a dreary office you've just rented, working day and night with a handful of employees just to break even.

As an academic, I'm just an amateur capitalist. Still, over the past 15 years I've started small ventures in both the U.S. and the U.K. In the process...