In 1984, Jim Koch left a $250,000-a-year consulting job to start brewing beer in his kitchen. "My dad told me this was about the dumbest f---ing idea he'd ever heard," the entrepreneur says, and, for a while, it looked like his dad was right.

In the early days of Koch's business, The Boston Beer Company, he was using a brewery in Pennsylvania to make his beer, but "I wanted to expand the brewery in Boston so I could make all my beer here," he tells CNBC Make It.

Koch, who was in his late 30s at the time, put together an engineering plan for the brewery and starting buying the equipment. But what he originally estimated to be an $8 million project quickly became a $15 million one.

At that point, "I'd already sunk $2 million" into it, he says. "So I had to decide: Am I going to take a risk that will probably sink the whole company and go for it, or do I pull the plug on it, write off $2 million and continue making my beer in what was actually a perfectly good brewery?"

He pulled the plug.