CHICAGO -- Model trains started as a hobby for David Swanson.

And like lawyer Brian C. O'Donnell's bad back, it led to the formation of a company that was never anticipated.

Similar firms were sparked by Bill Grabscheid's misfortunes making bathrobes and banker Rick Stallings' unusual interest in flags.

Call them accidental entrepreneurs -- business people who started out to do something else and somehow get sidetracked into businesses they now own or run.

In an age when business schools emphasize elaborate strategic planning and carefully followed career paths, and venture capital institutions require elaborate cash-flow forecasts and marketing studies, the accidental entrepreneurs are treated like anachronisms.

In fact, most of them admit they have trouble getting bank loans and finance growth out of existing cash flow or the salaries they earn at other jobs.

However, the universities are rediscovering entrepreneurship, according to Ivan O. Bull, University of Illinois professor and director of the Office of Business Innovation and Entrepreneurship Theory, which last fall sponsored a conference on that subject.

"When I graduated from school, a lot of students figured they would go to work for General Electric or General Motors and be taken care of for life," he said. But recent layoffs and corporate restructuring have caused an increased interest in entrepreneurship, Mr. Bull said.

"Entrepreneurship comes from inspiration, but it also comes from desperation," said Mort Kamien, professor of entrepreneurship at Northwestern University, a post created four years ago. "With high unemployment, you're going to have a lot of people become entrepreneurs because they have to."

The available literature on the subject indicates that entrepreneurs' motivation is not primarily wealth but lifestyle -- the desire to be one's own boss or see one's own invention or company succeed, said Mr. Kamien.

"Wealth is not the real goal, but it is an important measure of success," said Lloyd E. Shefsky, a Chicago attorney who represents many entrepreneurs and is completing a book on the subject.

In some cases, people converted avocations and hobbies into vocations -- often retail stores. People who invent something often form companies to manufacture and market the inventions, although more frequently the entrepreneur is someone who has the skills to exploit an invention by someone else.

Accidental entrepreneurship is a tough subject for scholars because there aren't always clear patterns. "At one time we thought entrepreneurs were unusual people, but now we think they are normal people who seem to be able to see opportunities other people can't," said Mr. Bull. "They have some expertise they use to exploit those opportunities."

Although most struggle in obscurity to make their companies work, a few such accidental entrepreneurs attain fame.

Probably best known was Ray Kroc, the man who built the McDonald's hamburger empire. He was a 52-year-old malted milk machine salesman in 1955 when he spotted the original McDonald's restaurant in San Bernardino, Calif., and talked the McDonald brothers into letting him become their franchise agent.

But Mr. Kroc said in a 1972 interview that his original idea was to make a fortune selling the malted milk mixers to a national chain of franchises. That was before he discovered how profitable the franchises could be and bought out the two McDonald brothers.

Mr. O'Donnell is probably more typical of the accidental entrepreneurs. He practices law in northwest suburban Barrington, Ill., and uses some of the income from that profession to finance the incubation of a company he formed to sell a snow shovel he invented for people with bad backs.

He was born with the ailment and invented the "Snow Bully" while shoveling his father's 144-foot-long driveway in Hoffman Estates.

He got a patent for the device while working as a gofer for a firm of patent attorneys while in law school. Since then, he has plowed $15,000 into the refinement and manufacture of his invention and is trying to convince the public he has a better mousetrap.

"My problem is that it hasn't snowed much around Chicago [in recent years]," Mr. O'Donnell said. "I'm hurting, but not as much as Toro."

Rick Stallings' bag is flags. After his entire banking division was eliminated, he decided to open a gift shop with his wife and in the process got stuck with a surplus inventory of Chicago Bears flags that he tried to sell back to the team. When the team said it wanted bigger flags to use as a backdrop at news conferences, he agreed to get them.

After a few televised news conferences, "the Bears called and said they were getting requests from fans who wanted flags," Mr. Stallings said. Now he runs his own company, Flying Colours USA in Carol Stream, Ill., which makes custom flags and banners for sports teams and corporations. His wife's gift shop in Glen Ellyn, Ill., turned out to be a flag store.

The transition from working in the family apparel business making bathrobes for children to operating his own firm that specializes in saving failing companies took almost 20 years for William H. Grabscheid.

"At age 24 [in 1956], I bought my own business and competed with my father," he recalled. "I ran that for close to 20 years before I finally failed." He bounced between jobs in the apparel industry before the urge to run his own company became irresistible again.

"But as I looked around, I found a lot that weren't doing too well," Mr. Grabscheid said. "So it became obvious I was not going to locate my ideal business for a while."

In the interim, he decided to use his expertise consulting with all those ailing companies he had considered buying and rejected. That led to jobs with big accounting firms. Early last year, he opened Grabscheid Group Ltd. to handle crisis management, turnarounds, bankruptcies and workouts with lenders.

"It's a long way from the apparel business," he said.

Oil also is a long way from cosmetics and glass bottles. Larry Buettner, who was selling glass containers for a major corporation, got interested in drilling for oil when he noticed the amount of money changing hands in the oil well investments that his friend Ronald Walblay, a cosmetics salesman, was selling on the side.

"His moonlighting activities were rewarding him handsomely, and we fantasized about going into the business ourselves," said Mr. Buettner. They did, and despite some dry holes, The Energy Group Inc. company they formed in Lincolnshire, Ill., this year expects to gross $5 million in revenue, Mr. Buettner said.

Mr. Swanson has managed to pursue two careers. By day he runs a team of computer troubleshooters for International Business Machines Corp. On the weekends, he runs GATS Ltd., which operates model train shows across the nation.