I like the writing style and assume this piece is well-intentioned. However, speaking as someone who had confidence problems all his life I think what he describes as (over-)confidence was actually confidence mixed with arrogance. I think confident people can not really be generalized, as confidence can be based upon many things. They might even be perfectionists. (no mutual exclusion here) But when arrogance and superiority feelings, and "I have done this for so long, I can do it in my sleep"-feelings kick in, it's where it gets dangerous.