Have you ever watched a talent show audition and wondered how so many dreadful performers could ever consider themselves good enough to win?
They overestimate their talent but remain free from embarrassment by being unable to recognise just how badly they’ve done. This combination of overestimation and selective blindness is a double burden which stops them from progressing (and has the side effect of providing us with hours of fun TV).
In order to realise how bad they are, they first have to understand what being good means: they have to learn how to perform better. It’s a paradox that happens in writing too.
You can read more about it Justin Kruger's and David Dunning's paper, Unskilled and Unaware of It: How Difficulties in Recognizing One's Own Incompetence Lead to Inflated Self-Assessments, which appeared in 1999 in the Journal of Personality and Social Psychology