What is risk?

In The Millionaire Next Door this question was posed by a professor to a group of MBA students. Being an entrepreneur! is what one student replied. The professor answered his own question with a quote form an entrepreneur:

What is risk? Having one source of income. Employees are at risk....They have a single source of income. What about the entrepreneur who sells janitorial services to your employers? He has hundreds of customers....hundreds and hundreds of sources of income.

That's the most I've ever typed entrepreneur in my life. Finished this book and I would recommend it, even if you don't think you'll ever be a millionaire.