Chronic
noun, の adjective
Overconfidence is in the nature of any problem that's chronic. No matter what you throw at it, it just confidently sticks around. Whether it's an illness or some other nagging issue, one thing's for sure: it's going to chronically and confidently bug you, forever.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
私は慢性胃腸炎を患っているんです。
I suffer from chronic gastroenteritis.