(Fortune Magazine) -- Gregg Fairbrothers wasn't born to business. He grew up in an academic household. "I didn't know a debit from a credit," he admits. Fairbrothers studied earth sciences at Dartmouth in the '70s, got his master's at Rutgers, and eventually moved to Tulsa, where he joined Samson, a gas driller, and earned his chops at the right hand of the company's "hard-nosed founder." He picked up an MBA, but that was "just to get the toolkit," he says. "I learned my business on the job."

Today, as founding director of the Dartmouth Entrepreneurial Network, Fairbrothers teaches a wildly popular course on entrepreneurship at the Tuck School of Business. As befits the professor's background, Introduction to Entrepreneurship is all about...