I’d say it’s more people who are repeatedly told they are smart can be very stupid.

Many of then might even be “smart”, but the important part is having unwarranted confidence.

Complicating things is that society rewards confidence way more than it rewards competence. If I’m honest about a lack of competence in a certain area but someone else lies during the interview, good chance they are going to get the job over me.

The reality is that everyone can be very very stupid, and so long as each and every one of us is willing to accept and recognize our weakness we aren’t as likely to be assholes.