The stories of failed moral and ethical leadership keep coming. Jon Corzine’s brokerage firm MF Global is being investigated for illegally diverting $600 million in customer investments. Rajat Gupta, former Goldman Sachs and McKinsey consulting rock star, is arrested for insider trading. And Herman Cain’s quest for the presidency has now been sidetracked by multiple accusations of sexual harassment while head of the National Restaurant Association.

You probably wonder, “What were these guys thinking?” But none of these stories surprise Nitin Nohria, dean of the Harvard Business School, who spoke yesterday at Tedx New England about the pitfalls of “moral overconfidence.” Nohria’s work with new CEOs has convinced him that leaders consistently underestimate the difficulties of creating the right moral and ethical values in their organization. “We all like to think of ourselves as better than the average person,” said Nohria. “But each of us is capable of acting in ways that shock us.”

Nohria asked his audience of almost 300 smart people (who else goes to TEDx?) if they would make the right choice in a particularly challenging scenario he presented. Not surprisingly a majority of hands went up. But Nohria pointed out that research has consistently shown when given power two-thirds of us are very likely to make immoral decisions in difficult circumstances. So we live with this kind of moral overconfidence that the kinds of mistakes that bring other leaders down wouldn’t happen if we were in charge.

In the end, said the Harvard dean, confidence is something to fear as a leader when it comes to morality. “We need leaders who know they are fallible, who have moral humility,” he said. The question he left us with is: how would you cultivate your own moral humility? Certainly the first step is being aware of this trap.