He spent two years going back through the data and charts, writing his new book, "The Map and the Territory."
"It became very apparent to me that we misunderstand how systematic fear is," he said.
The fear that led to panic selling and the euphoria that inflated the housing bubble were not factored into the Federal Reserve's computer models.
Greenspan himself believed irrational behavior could not be projected or analyzed.
Now, he says, "I was wrong."
"You think you can put human behavior in a model or in an equation?" Mason asked.
"In fact, you can measure it," Greenspan replied. "Because if you look at the business cycle, for example, euphoria drives it about, and then fear collapses it. And you can take one example after the other, and they look alike."
Long before he was maestro of the economy. Greenspan studied music at Juilliard. He toured for a year with the Henry Jerome Swing Band, playing saxophone and clarinet.
Greenspan pulled out his original clarinet, which dates from the 1940s.
"Boy," he said, "this brings back memories. I'd blow it, but the problem is, I remember how it used to sound. And I just try to remember that."
Greenspan saw he was never going to be a great musician.
"I mean, I had played next to Stan Getz -- I was 16, he was 15 -- and I played for a year side-by-side with him in a band. And he was basically pretty much determined I was gonna become an economist!"
But it did lead him to his wife, Andrea Mitchell.
"In fact, what originally attracted me to her was she liked the same music I did."
Greenspan and the NBC News correspondent have been married for 16 years.
She told Mason that Greenspan is an obsessive writer.
"Compulsive. He is morning, noon and night, to the point where we'd be driving to the tennis courts and he'd be looking at some manuscript and ask me to drive so that he could edit copy during the red lights."
"If you get an epiphany, you don't wanna lose it," he explained.
At the Federal Reserve, there's about to be another changing of the guard. Janet Yellen, nominated to be the next head, served under Greenspan in the '90s.
He said, "She's a very intelligent woman. I'm glad to see her as the first woman Chair of the fed. It's long overdue."
He runs a consulting business now, still keeping his eye on the economy. At 87, there is nothing retiring about Alan Greenspan.
"Is that an option?" Mason asked.
"Is what an option?"
"I don't know what it means," Greenspan responded. "I mean, what do we do, stop thinking?"
For more info:
- "The Map and the Territory: Risk, Human Nature, and the Future of Forecasting" by Alan Greenspan (Penguin); Also available in eBook and Unabridged Audio CD formats
- "The Age of Turbulence: Adventures in a New World" by Alan Greenspan (Penguin); Also available in trade paperback and eBook formats