(Mark Lennihan/AP)

One thing is refreshing about the way J.P. Morgan Chase has handled its gigantic $2 billion trading loss: It admitted that it screwed up.

This is novel on Wall Street. Over the last few years, we watched titans at AIG, Merrill Lynch, and Citigroup walk away with nine-figure paychecks while leaving their firms in tatters, indicating no regret whatsoever. When Lehman Brothers collapsed in 2008, CEO Richard Fuld blamed competitors, the press, and the government, but largely exempted himself for Lehman's massive mistakes. Goldman Sachs has issued one legalistic, self-righteous explanation after another in response to criticism of its Machiavellian habit of putting its own interests ahead of customers. Has it ever done anything wrong? Banish the thought.

J.P. Morgan seems to have screwed up big-time, by losing a bundle with a strategy that was supposed to "hedge" risk but ended up inflating it. But CEO Jamie Dimon has at least gone out of his way to say the huge loss wasn't caused by external forces, but by bad decisions right inside his own firm. He called the hedging strategy that led to the loss "flawed, complex, poorly reviewed, and poorly executed."

"We made these positions more complex and they were badly monitored," Dimon told analysts on a conference call. In an adjectival flurry of self-admonition, he added that the mistakes were "egregious" and "self-inflicted."

Dimon didn't go as far as to fault himself directly, but he improved on the usual vague and backhanded acknowledgement that "mistakes were made." He spoke in the active, not passive, voice, and used the pronoun "we" instead of reading elliptical, carefully orchestrated remarks designed to acknowledge a problem while denying that any actual person could be responsible.

Some critics, including MIT economist Simon Johnson, say Dimon should fall on his sword and resign. Johnson is an expert on finance who plumbed Wall Street's culture of greed in his acclaimed book 13 Bankers, and he rightly points out that J.P. Morgan's losses, which still haven't been fully explained, come at a tepid time in the markets, raising questions about how the too-big-to-fail bank would fare in a genuine crisis.

But CEOs shouldn't be fired for making mistakes. What they should be fired for is denying their mistakes, or blaming others for them. Dimon has more explaining to do, but by putting the blame for the loss squarely on J.P. Morgan, he's showing that he has identified a problem and taken steps to fix it. You can only do this if you recognize your own role in what went wrong. What has mostly happened on Wall Street, by contrast, is that CEOs deny their own culpability and look for somebody else to blame, which means the problem doesn't get fixed, it just gets buried.

Making a mistake, acknowledging it, and doing what's necessary to fix it is actually a terrific learning experience that heightens sensitivity to what could go wrong. Instead of running adverse scenarios using computer models, Dimon is dealing with a real-life adversity, including the human frailties, market pressures, and public criticism that don't always show up in simulations. Assuming that Dimon is telling the truth and acknowledging the whole problem, he's likely to emerge from this fiasco wiser and more capable of spotting similar problems in the future.

Many of our most admired business leaders, including Steve Jobs, Warren Buffett, Jeff Bezos of Amazon, and Jack Bogle of Vanguard, got smart by making mistakes and learning from them. When something goes wrong, we often expect heads to roll. But instead of generating greater accountability, an intolerance of mistakes tends to encourage evasion and cover-ups. For once, somebody on Wall Street is taking responsibility for the bad decisions made under his watch. That's the way a CEO is supposed to act.