They say all you need is passion to start a business. I say that's crap. Respectfully, of course.

People who are too passionate about their business create a job for themselves, not a business.

Take, for example, a young person finishing school who is encouraged to start a business around 'something they are passionate about.' Having enjoyed photography as a hobby, she might open a photo studio and offer to shoot everything from weddings to food ads to tee ball teams. She's good at what she does because she is passionate. Customers like her because she is passionate. Subjects give her their best smile because she is passionate. Pretty soon, all of that passion starts to define the business, and the studio becomes synonymous with the owner's passion.

Then the owner decides to take a vacation, and like the air being sucked out of a room, the business dies off without that passion to keep it going.

The photographer starts to tire of the histrionics of nervous brides and the constant wailing of newborn babies being forced to pose. Pretty soon, she falls out of love with photography and wants to get out, but she has nothing to sell because the business is her passion for photography. Plus, she's spoiled her favorite hobby.

Compare the passionate photographer to the owner of the School Photo Company in Albany, New York. Also a photo studio, the School Photo Company is a real business, not a job masquerading as a business. The School Photo Company specializes in taking school pictures. Parents want pictures every year, so the company has a repeatable model. It has a formula for getting a classroom of students to sit down and smile within eight minutes, which it teaches to all of its young photographers. All the company does is school photography. It doesn't dabble in weddings or babies or magazine covers. Given its focus, principals talk and recommend the School Photo Company to one another. The business grows by word of mouth and is not dependent on any one person.

Now, you might argue that the School Photo Company sounds like a boring place for a new photographer to work. Fair enough, but don't confuse having a passion with having a sellable business.

If you really love something, keep it a hobby, not a business.

John Warrillow is the author of Built to Sell: Turn Your Business into One You Can Sell. He has started and exited four companies. Most recently John transformed Warrillow & Co. from a boutique consultancy into a recurring revenue model subscription business, which was acquired by The Corporate Executive Board. In 2008 he was recognized by BtoB Magazine's 'Who's Who' list as one of America's most influential business-to-business marketers.