Business leaders are to employees what Brad and Angelina are to tabloids: subjects of endless fascination and speculation. Even CEOs who view themselves as open books can count on staffers scouting for a subtext. Employees read the leader's moods, parse his statements, and analyze his sudden predilection for silk pocket squares. Their favorite source of executive skinny: the horse's confidante's mouth.

Leadership scholars talk about kitchen cabinets--informal advisory groups that act as sounding boards for top executives. In most kitchen cabinets, one member ranks first among major appliances. That person--who is often seen in the CEO's office or at his side heading out to lunch--may be the company's second-in-command or simply the boss's best friend. Even when the role of confidante isn't official, everyone in the company knows who it is.

What CEOs spill into confidantes' ears, others are eager to extract. Employees worried about their own or the company's performance may hesitate to approach the leader. Instead they ask the confidante to cast oil upon their troubled waters. "Is Estelle bringing this new guy in because of my screwup?" "How come Armin doesn't drive the Jaguar (NYSE:F) anymore? Are we in trouble?" Employees also hunger for informed interpretations of the leader's mental state. "Is Max okay? I can never tell if Max is okay."

For CEOs--particularly those so brilliant or bellicose as to be intimidating--such trustworthy liaisons are enormously valuable. Confidantes carry the boss's message into the cubicles and offices of the staff at large, thereby softening black-and-white pronouncements with shades of gray, absorbing some of the shock in tumultuous times, and humanizing the glorious leader in followers' eyes. And because confidantes collect information as well as dispense it, they are excellent takers of organizational temperature.

That role is fine with most confidantes, who genuinely like the CEO and want him to succeed. Many also relish politics and enjoy the stature conferred by proximity to power. And, of course, it's flattering when one's opinions mean so much to so many.

But such arrangements work only if the rules are clear. CEOs should not treat their confidantes as flacks or mouthpieces, but rather as interpreters adept at reconciling the public and private faces of leadership. Trust--between leader and confidante and between confidante and staff--must be maintained. The CEO must never ask his confidante to lie. And he should avoid deliberate ambiguity or outright dissembling that could leave his confidante flailing before interrogators. "There are times I feel like Tony Snow," one CEO's best friend told me recently. "Only I don't have any talking points. So I'm afraid of saying the wrong thing."

Finally, CEO and confidante must agree when conversations are taking place under Las Vegas rules (what happens in the corner office stays in the corner office). The best confidantes are part psychologist, part diplomat. Business leaders must always remember which part they're talking to.

Leigh Buchanan is an Inc. editor-at-large. She can be reached at lbuchanan@inc.com.