CHICAGO (TheStreet) -- The many struggles of entrepreneurship have been well covered in news stories and personal blogs: the late nights, the financial uncertainty, the pressure to attract customers or clients. Starting a venture is inherently risky and therefore inherently stressful.And yet, starting up and running your own business also comes with some very tangible rewards. A study by the University of Pennsylvania's Wharton School of Business found a strong correlation between entrepreneurship and happiness, one that held even if the start-up in question wasn't phenomenally successful. The study, by Wharton management professors Ethan Mollick and Matthew Bidwell, surveyed 11,000 graduates of the Wharton MBA program, asking them to rate their happiness with their career overall, their current job and their work-life balance. It should be noted that this was not a particularly entrepreneurial-minded group: The majority took jobs in banking, consulting or financial services after completing their degree. But during the course of their careers, about 20% of the graduates ended up starting their own businesses. In general, the study contradicted the old saying that money cannot buy happiness; the more money someone earned, the happier they tended to be. The older respondents also tended to be happier than the younger ones. But what really surprised the study's authors was the role entrepreneurship played in a person's overall career satisfaction. If money really was the key to happiness, you would expect the high-level execs at financial firms to rate themselves as happiest. But that wasn't the case. Grads running their own businesses ranked themselves happier than all other professions, regardless of how much money they made. (A few consultants came in at the top as well). "We were surprised that entrepreneurship was such a dominant factor," Mollick says. After all, one of the reasons people attend a school such as Wharton is for the credentials and contacts that will get them hired at a prestigious financial or consulting firm. But the study made clear that for a variety of reasons, a stint as an entrepreneur is becoming an increasingly common part of an overall career arc. "People tend to view entrepreneurship as an end state," Mollick says. "That doesn't seem to explain what people actually do." In the real world, people switch back and forth between being an employee and running their own business, alternating working for themselves with working for others. Contrary to the media hype that surrounds Silicon Valley start-ups, most entrepreneurs are not flooded with venture capital; the majority don't even have employees. Making a living is a best-case scenario; for others, it can be a matter of barely scraping by. Of the Wharton grads surveyed who started their own businesses, only 56% made a profit. And yet, the fact that nearly half of the people who started their own businesses were not financially successful did not drag down the overall happiness rankings for all entrepreneurs. Could it be that simply having entrepreneurial experience -- even if it didn't pan out -- contributed to overall career satisfaction? Mollick and Bidwell are continuing to crunch their numbers to find out. Grads running their own businesses also rated themselves higher than any other profession when it came to work-life balance. "Entrepreneurs are working really hard," Mollick says. "But there's a sense that they have control over their own time, even if they're putting in a huge number of hours." An entrepreneur can choose to take a break to attend a daughter's soccer game or son's school play, even if that means working late into the night afterward. Perhaps the most important takeaway from the Wharton study is the unpredictability of any career in the current economic climate. Everyone -- even the graduates of a prestigious MBA program -- should be prepared to reinvent themselves professionally at some point. It's also a reminder that despite all the risks that come with starting your own business, the experience can come with some very real, life-changing rewards.