One more readily accepts instruction from proven pros with the right expertise, but the delivery method of such sage advice impacts how it is received.
In this complex world of ours, there are certain situations in which there are definite right and wrong ways to behave. You don't, for example, expect a good outcome from stepping in front of a speeding 18-wheeler. Climbing into the bears' habitat at a zoo is another all-risk, no-gain move.
Many more scenarios have dos and don'ts which are learned from those more experienced, or trial and error (in which case you become your own voice of experience). Whether or not to be a daredevil in itemizing tax-deductions, for instance, or to treat the highway speed limit as an optional guideline.
One more readily accepts instruction from proven pros. Credentials are good, but directly-witnessed expertise generally instills more trust and respect. I'm more likely to take pointers from a chest radiologist on my team who repeatedly demonstrates to me how brilliant he is than from some guy I've never met whose name is on a few textbooks and/or the departmental roster for the Cleveland Clinic. Granted, I'm not going to be dismissive of the latter individual's two cents.
The delivery method of such sage advice impacts how it is received. If I meet the Cleveland guru at a conference and pick his brain for the answer to a question that's been on my mind, I'm more likely to take his words to heart than I am if I randomly come across them in a journal. And a hell of a lot more predisposed than if he's on a government panel that issues a new edict on how I must practice my profession.
At least some of the time, those impressive credentials and positions of authority are fairly earned by innate talent, developed skill, and/or years of experience. Such experts may understandably be proud of their accomplishments. They may have gotten accustomed to having their opinions go unquestioned, and even developed a never-in-doubt demeanor as this can be helpful in establishing and maintaining their rep.
It is small wonder, then, that some go a step further, becoming sufficiently accustomed to the role of unquestioned authority that they start considering themselves the smartest guys in the room in areas tangential to their actual expertise.
I'm not talking about rampant egomania, like the chest maven mentioned above starting to insist he's also the best in the department at neuro, peds, investment, his golf swing, and needlepoint. Rather, for instance, deciding that he's come up with the best-ever format for chest-CT reports - and he's going to let everybody else know when their dictations aren't up to his standards. Or pushing for a policy that everyone must conform to his specifications.
Such individuals may be aware of how they're coming off, and/or are unconcerned that many of their peers consider them to be complete anal orifices. Conversely, some of those who cannot avoid routinely rubbing elbows with the know-it-all may not mind his or her overweening ways, whether out of abundant tolerance or because access to the intellectual narcissist's skills is deemed a sufficient tradeoff for his/her attitude.
Like genuine personality disorders (not just narcissists), the condition tends to be egosyntonic; that is, the know-it-all is unlikely to think he is the one with a problem, and those trying to point this out are likely to be dismissed as too dim to recognize his brilliance or even envious of it. Often, the only solution is containment, whether physical (sticking the genius in his own remote reading room), or social (as per oft-given parental advice, "Don't play with him, then!").