John Bogle on the Go-Go Sixties

Q: What was your biggest mistake? Bogle: When I was 38, I became head of Wellington Management, and I did an extremely unwise merger. I got wrapped up in the excitement of the go-go era, and the go-go era ended. As a result of that stupid decision, I got fired. The great thing about that mistake, which was shameful and inexcusable and a reflection of immaturity and confidence beyond what the facts justified, was that I learned a lot. And if I had not been fired then, there would not have been a Vanguard. 

~ John Bogle, "Questions For John Bogle," Fortune, December 24, 2007