The brain is a funny thing, and sometimes we "know" things which aren't true.
In particular we can be "prompted" to see and hear things that are not there. Particularly when when data are messy and noisy, we can be influenced by mental framing to make those data fit what we expect to see or hear.
So "shared knowledge" can be completely false, but can reinforced because people expect it to be true, and so experience it. Sort of like the emperor's new clothes.
Watch the video below by Simon Singh, the science writer and ex-Guardian columnist, and be prepared to hear something which does not exist.
So what is the implication for Knowledge Management? The implication is that you must test collective knowledge against reality. Don't believe something, especially when the data are poor, noisy or ambiguous, just because other people tell you in advance what you will see. Keep your mind open until you have tested the knowledge against reality.