True scientific demonstration involves convincing an observer who is outside the process, particularly one not deeply and emotionally enmeshed in it. - Robyn Dawes

The situation is very simple. Familiarity leads to availability and often to accuracy as well; hence availability is used as a cue to accuracy.
The problem is that mere assertion and repetition also leads to availability, whether or not this assertion and repetition involve reality, as familiarity generally does. Thus, the “big lie” of Nazi propaganda minister Joseph Goebbels was based on the idea that if something is repeated often enough, people will believe it—in large part simply because they have heard it before…
Goebbels apparently believed that providing a credible source, for him the German national government, was a critical component in having the repeated statements believed. Subsequent research has shown that the credibility of a source is not a necessary condition to develop beliefs…
Worse yet, mere repetition—which creates an availability bias due to familiarity, can also make people confident of their own decision making in the absence of any feedback that they have made good decisions.

Unfortunately, there are many irrational conclusions and beliefs in our culture from which to choose. Those analyzed at some length—and as precisely as possible—are those with which I am most familiar. With public opinion polls indicating that more people in the United States believe in extrasensory perception than in evolution, it is not surprising that examples abound.

Many people operate as if there are two separate and equal sources of information—the self and others, where the number of others is irrelevant. The result is a “truly” false-consensus effect in the context of knowing one’s own plus a certain number of others’ responses.