The most common way to become a millionaire, according to someone who studied over 100 of them

Jaime Masters, author of "The Eventual Millionaire: How Anyone Can Be an Entrepreneur and Successfully Grow Their Startup," hoped to change her lifestyle when she was 24 years old.

Masters, who wrote her book under the name Jamie Tardy, was over $70,000 in debt and hated her job as a project manager for a company that installed computer equipment.

"I felt stuck, because I knew we were in debt and I couldn't quit my job because of the choices I had made," she writes.

Instead of giving up, Masters began to study and interview people who had already reached that goal.

Based on research from Thomas Stanley in "The Millionaire Next Door," and the many "first-generation rich" millionaires she interviewed, she come across commonalities that led their success. (You can read some of her case studies on her website.)

She writes that the one proven way to become a millionaire is not by investing, nor is it real estate. Instead, more millionaires have made their money by owning their own business than by any other means.

They usually have an idea or a product in mind to help them grow their wealth, and they're going to be the one to sell it. It can be just about anything. For instance, Masters spoke with Brad Deal of Sticks and Stones, which creates custom wall art; Hanny Lerner of Mod Restoration, an upholstery company; Craig Wolfe of CelebriDucks, which makes rubber duckies that look like celebrities; Joy Gendusa of postcard company PostcardMania; and Derek Sivers of CD Baby, an online CD store for independent musicians.

Instead of doing it under someone else's watch or time, the millionaires were able to do what they wanted, manage their own priorities, and do something they love.

"When you own your own business you control your own destiny, you control the work/ life balance, and you take risk but also reap the rewards," writes Masters.