What happened this time, and how did it happen? You can parse the stories about how the bank's risk-management people were really incentivized to load up on risk, or digest the accounts of how JPMorgan's financial wizards engineered mind-bendingly complex means of limiting their vulnerability to troubles in Europe. But the simplest answer is the most pertinent: It's extraordinarily complicated. So complicated that the trades involved exceed the intellectual bandwidth of would-be regulators, which is another way of saying that taxpayer-ensured deposits should not be allowed in such gambling.

"They can't explain this," said Sheila Bair, the former chairwoman of the FDIC, when I called her last week to get her take. She ran through JPMorgan's evolving explanations for what had gone down -- how the trades were a hedge against securities in its portfolio, then a hedge on loans on its books, or maybe a hedge for its entire banking operation -- and dismissed each as inadequate and troubling. "It makes no sense whatsoever."

Sheila Bair has spent her distinguished career peering into finance and regulating financial institutions. She has held senior posts at the Treasury Department and at the New York Stock Exchange. She held a seat on the Commodity Futures Trading Commission. At the FDIC, she was among the earliest officials to sound a warning about the growing risks of subprime mortgages on banks' balance sheets. If she can't get clear on what happened, how is anyone supposed to?

The opacity around JPMorgan's losses underscores the fundamental problem: Mega-banks are prone to do diabolically complicated things with their money. And their money has a tendency to become our money when they find themselves staring at losses big enough to pose a risk to the broader financial system.

Bair was careful to note that JPMorgan's losses, however serious, do not not appear to be anywhere close to big enough to threaten the solvency of that institution, let alone the soundness of the broader financial system. Still, the fact that these losses appear to stem from gambling inside the bank, using depositor funds that are ultimately ensured by taxpayers, highlights how the same incentives and regulatory gaps that nurtured the financial crisis of 2008 remain with us today.

"It really shows that most of the problems that we saw during the last financial crisis have not been fixed yet," Bair said.