People are individually rather limited thinkers and store little information in their own heads. Much knowledge is instead spread through the community—whose members do not often realise that this is the case.
(Steven Sloman and Philip Fernbach) call this the illusion of understanding, and they demonstrate it with a simple experiment. Subjects are asked to rate their understanding of something, then to write a detailed account of it, and finally to rate their understanding again. The self-assessments almost invariably drop. The authors see this effect everywhere, from toilets and bicycles to complex policy issues. The illusion exists, they argue, because humans evolved as part of a hive mind, and are so intuitively adept at co-operation that the lines between minds become blurred. Economists and psychologists talk about the “curse of knowledge”: people who know something have a hard time imagining someone else who does not. The illusion of knowledge works the other way round: people think they know something because others know it.
From a review in the Economist of “The Knowledge Illusion: Why We Never Think Alone” by Steven Sloman and Philip Fernbach