What causes the lunatic to demand that ideas not be subject to scrutiny—and in particular that they not be contradicted? No one knows. It may be part… - 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.

Believing you’re good at something just because you do it—without any information that you’re doing it well—is indeed irrational.

The limitation of the story to a single sequence and the essentially ad hoc nature of causal attributions call into question the whole procedure of using stories as evidence, and of thinking that they establish causality or patterns of reasons.