A college professor got the chance to invest in a company that would go on to be worth $6.8 billion. He passed because the four guys pitching him were still in school and wouldn't work on it full time. He calls it the worst financial decision he's ever made. Then he spent the next six years figuring out what he got wrong, and what he found goes against most of what you've been told about starting a business. The company was Warby Parker, and it started the way a lot of good ideas do, with…