I see this misunderstanding all the time. A manager (people manager or project manager) gets bent out of shape because person X can do something and person Y with the same job title can't do it. Sometimes this is for bad reasons: poor documentation practices, or person X protecting their turf or their job security by hoarding information. But just as often it's because person X has a ton of relevant knowledge and experience that is a great asset to the company, and person Y maybe has less experience, or their experience and knowledge are concentrated in a different area. Often the fault is with the people or project manager, who is failing in their responsibility to understand and manage the company's talent effectively.