I have already posted about some of the illusions that we need to be aware of in KM.
Here's a graphic demonstration of another illusion - that what we perceive, may not be there at all, and that when data are messy, we can make them 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.
Simon is explaining this in the context of the Big bang, but it holds in many other contexts.