NPR: When was the last time Americans owed as much as they do today? Scary answer.

... David Beim has a much more profound reason why banks shouldn't lend. He shows me something on his computer.

David Beim: Ok, so here is a picture, a graphic, and a chart that goes back to 1916 and up to...

Alex Blumberg: We’re in his office, and we’re looking at a graph, and it's, basically, a measure of how much debt we the citizens of America, are in. How much we all owe--on our mortgages and credit cards and auto loans--compared to the economy as a whole, the GDP. And for most of history, the amount we owed was a lot smaller than the economy as a whole.

This ratio, household debt to GDP bounces along around between 30 and 50 percent, for most of the '30s and '40s 50s, 60s, and 70s, right into the 80s. Then it breaks through 50 % in the 80s, starts heading up in the 1990s. And then ...

David Beim: From 2000 to 2008, it just goes, almost a hockey stick, it goes dramatically upward.

Alex Blumberg: Like a rocket.

David Beim: It hits 100% of GDP. That is to say, currently, consumers owe 13 trillion dollars when the GDP is $13 trillion. That’s a $100 trillion owed by individuals. That is a ton.

Alex Blumberg: I'm going to ask a leading question, because I’m looking at a graph right here. Tell me professor, has there ever been a time where we owed that much before?

David Beim: I’m glad you asked me that. And guess what? The earlier peak, which is way over on the left part of the chart, where debt is 100% of GDP, was in 1929. This is a map of twin peaks. One in 1929 and one in 2007.

Alex Blumberg: Does that chart scare you?

David Beim: Yes. That chart is the most striking piece of evidence that I have that what is happening to us is something that goes way beyond toxic assets in banks, it’s something that had little to do with mortgage securitization, or ethics on Wall Street, or anything else. It says the problem is us. The problem is not the banks, greedy though they may be, overpaid though they may be. The problem is us. We have over-borrowed. We have been living very high on the hog. We are, our standard of living has been rising dramatically over the last 25 years, and we have been borrowing to make much of that prosperity happen....