Lewis Schiff, adviser to the superrich and founder of the private wealth specialty firm Advanced Planning Group, coauthored the recently released The Middle-Class Millionaire: The Rise of the New Rich and How They Are Changing America. Schiff defines "middle-class millionaires" as those with a net worth of between $1 million and $10 million who earned their wealth rather than inherited it. They are people, the author says, who live a fundamentally middle-class life, yet are exerting powerful influence on society.

Schiff and his coauthor, Russ Alan Prince, surveyed more than 3,600 middle-class-millionaire households for their book. Schiff spoke with U.S. News. Excerpts:

How does a middle-class millionaire approach retirement?

I think the traditional retirement concept of stopping work and living on the assets you've accumulated is something the middle-class millionaire is redefining. The notion of retiring at 65 is not something you necessarily hear from them.

Folks who are succeeding in America are knowledge workers, in financial services or creative services, where their brain is their No. 1 asset. The body is healthier for longer and longer periods, and now that the body isn't failing and you have the technology where you can get on a yacht and continue to do business, they might just look to scale back and not retire, because their bodies are up to it anyway.

What kind of person becomes a middle-class millionaire?

They on average work 70 hours a week and take fewer vacation days. They show perseverance in the face of adversity. They've had more failures in their professional life, but what's interesting is what they do in the face of failure. They observe information in a more savvy way and tap into the flow of information capital, and they know how to leverage this enlightened self-interest.

You talk about persevering in the face of adversity. What does that look like to this group?

These are people who have had an average of three career setbacks, and three quarters of the group we surveyed said that each time, they've come back in a different way. Persevering in the face of adversity is easier said than done, but it's a distinguishing characteristic.

The middle-class millionaires we spoke to said that failure and defeat are crushing no matter who you are, but some of them will say, "I have to rectify this because I prize financial independence above all else."