Complete Self-Confidence

Complete self-confidence is not merely a sin; complete self-confidence is a weakness.  ---  G. K. Chesterton, in Orthodoxy, 1908.  Though Orthodoxy was written as a Christian apology, this quote has an especially  definite and profound secular value.

Most truly intelligent people I know have incomplete self-confidence. The self-confidence allows them to approach extremely difficult problems, while the incompleteness delimits first guesses and jumps toward a firmament of knowledge without proof.

Complete self-confidence often comes with a built-in orthodoxy allowing easy conclusions based on easy thinking.

Complete self-confidence offers self-assurance, thus casting self-doubt, introspection, and rigor aside.

Complete self-confidence weakens the holder’s  grasp on reality in favor of an internal mechanism of an unmerited self-righteousness.  

Complete self-confidence weakens the need for rigor in acceptance or belief in almost everything.

Complete self-confidence allows emotion to control reason.

Students with complete self-confidence have already stopped learning, i.e. no more is needed.

Adults with complete self-confidence edge up to the lunatic fringe.

Finally... 

No self-confidence, on the other hand, invites paralysis.  It is also a sin and even more a weakness.