(MONEY Magazine) – Your typical CEO thinks it's his job to keep his company's stock price moving steadily upward. He's wrong, says Michael Jensen, emeritus professor of finance at Harvard Business School: When stock prices get too high, CEOs should be talking their stocks down, not up. We spoke with Jensen about his intriguing take on value maximization

Q. What's so bad about having an overpriced stock?

A. It's like organizational heroin. It feels great. You're on TV. Your stock options are going through the roof. Banks are throwing money at you. But when a stock gets substantially overvalued, it requires financial performance that management can never deliver. This drives managers to lie, cheat and steal.

Q. So in some sense the stock makes them do it.

A. I do believe that there are crooks out there. But the forces in the late 1990s were do great that even perfectly honest managers were committing fraud out of desperation, in the hope that if they could just get though this quarter someone would find gold on the back 40 acres.

Q. How do u know if a stock is overvalued?

A. I tell managers. "If you're tempted to manipulate the numbers to justify the stock price, it is overvalued". You can't look up the degree of overvaluation in the Wall Street Journal, but that doesn't mean we can't tell. The ones most likely to know are managers desperate to deliver the performance needed to prop up the price. --DAVID FUTRELLE