The over confidence I've observed in myself is the standard dev "of course my code works right" stuff, especially as I've gotten more senior. The way I protect myself against it is on every PR I have a standard template I make myself write out : not just what am I changing and why, but how did I test it and what docs needed updates. The act of writing out the testing has made me realize stuff I missed, and more than once I found a bug when I went back to do the testing.
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