As a boss, you must be knowledgeable and bright, but demonstrating expertise in your field is no longer your most critical professional asset.

By Linda A. Hill and Kent Lineback, contributors

FORTUNE -- Imagine you're a manager in the IT department and you're chatting one day in the corridor with a few software engineers who work for you. One of them turns to you and asks a technical question. After a moment's hesitation, with all eyes on you, you say, "I don't know," and immediately one of the other people provides the answer.

Afterward, you realize that brief episode left you feeling off-balance, as though you'd failed a test in front of the people who look to you for help.

Did you know the answer? Not really. It concerned some recent technical development, one of dozens in your field. You try to keep up, but it's just impossible. Still, it didn't feel good.

Can you see yourself reacting that way in those circumstances? Is it difficult for you to say, "I don't know" or "I'm not sure," or to ask for information and answers in the areas you manage -- the areas you're supposed to know a lot about?

As the boss, are you supposed to be the one who knows the most, the smartest one, the most able? Is that what people expect of you because you're in charge? More