Experienced professionals, whatever their field, often serve as role models, mentors and/or partners to those of us who are still on our own learning pathway. These people have "been there, done that," which is to say they have already trodden the road that we're on, and they've learned about its twists and turns and the hazards along the way. That's why we learn from them, and we observe them to see how they do what they do.
We need to remember, though, that even the most consummate professional might have reached a plateau in their own learning and skills development. This is particularly true if they have come to the conclusion that they now know everything there is to know about their chosen profession, and that consequently there is nothing more that they can learn. Sometimes, even top professionals can become complacent or lazy.
Leadership never emerges from blindly following some guru, no matter how impressive their qualifications or track record. Therefore, we must always be prepared to challenge the professionals, even in their own field of expertise. Look at it this way: if I question a pro, then one of two things could result. First, she might explain to me what she's doing and why, and I stand to learn from that. Alternatively, he might bluster and get defensive, in which case I know he's either being complacent or lazy and I should beware of his approach.
Barry Rand at Xerox once said that if you have a "yes man" working for you then one of you is redundant. As a leader, encourage your people to ask questions and to challenge you when they don't understand why you're doing something. Good leadership encourages everyone's personal and professional evolution.