The Embarrassment Factor
Five people on a committee. Each has an impressive background and each is assertive.
No. In this instance, one of them can make a reasonable claim to having more expertise than the others as well as more experience in the subject matter. The others know it and so, from the beginning, they may give great deference to the unofficial expert out of respect and, in part, out of a desire not to be embarrassed. It is also easier to avoid culpability for any mistakes by deferring to the expert in the room.
Unfortunately, if the "expert" turns out to be less than capable, the passive committee members have fostered a problem. Their fear of embarrassment has turned the committee of five into a committee of one.