> I’ve very recently found that a lot of very smart people are still quite capable of doubling down on stupid

Being consistently the smartest person in the room can lull some to believe they are smarter than everyone, everywhere, every time.

Sometimes the lack of intellectual humility is an independent personality trait, but I've encountered a number of very smart people that held really weird beliefs which bordered on conspiracy thinking, but was self-reinforcing because they thought everyone else was not smart enough to cotton-on to "the man" (one believed in over-unity energy,the other one is basically synthesizing a new religion(/cult?) by gaining "insights" into "correct" aspects of multiple existing ones, whose current practitioner's "get it wrong" in one way or the other.)