A Wharton professor reveals 'the worst financial decision' he ever made - and what it taught him about success

In 2009, one of Wharton professor Adam Grant's students approached him about an investment opportunity. He and three friends were thinking about starting a company where they'd sell glasses online.

"I thought they weren't going to succeed because at every turn they played it safe," Grant tells Business Insider. So he decided not to invest.

As it would turn out, this strategy led eyewear e-commerce company Warby Parker to become a billion dollar brand investors reportedly begged to be part of - and not getting in on the ground floor is "the worst financial decision" Grant says he ever made. Now he has his wife handle their investments.

Not one to take failure sitting down, Grant writes in his new book, "Originals," that he was determined to figure out where he went wrong - or, more importantly, where Warby Parker went right. All roads lead back to the cofounders playing it safe, he says.

As Grant notes, Warby Parker's cofounders were working on their company while taking classes at Wharton. When Grant suggested they drop out to focus their efforts on the business, the cofounders were unwilling. They even all had job options lined up for after graduation in case the launch didn't work out.

While taking big risks like dropping out of college or quitting a job are often lauded when starting something new, Grant tells Business Insider, "hedging their bets actually gave them the freedom to try to do something original."

"Knowing that they had something to turn to led them to say, 'You know what? We don't have to race to market. We're going to make sure we do this right,'" Grant says.

As a result, he says Warby Parker's cofounders were able to be cautious around branding, and they spent more than six months testing 2,000 names to find something unique, sophisticated, and without negative associations before deciding on Warby Parker.

"If you were feeling pressure to make this business succeed because you had nothing else in the hopper, you probably would have gone to market a lot sooner," Grant says.

And only after spending weeks trying to figure out how they would get people to buy glasses online did the cofounders come up with their "sensible" Home Try-On program. The program allows users to test just the frames to see if they fit and look good, and it works better than free returns because Warby Parker saves money by not having to create custom lenses and being able to reuse sample frames, Grant says.

"By the time we were ready to launch, and I had to make the decision this was something we were ready to do full time, it didn't seem risky. It didn't feel like I was taking a big leap of faith," says Warby Parker co-CEO Dave Gilboa in Grant's book.