Why do people ____?

The other day, some­one did some­thing I didn’t ex­pect. It was some­thing many peo­ple have done be­fore; some­thing that I thought of as very nor­mal, but that I in no way un­der­stood and had not pre­dicted.

As I said, this had hap­pened many time be­fore, so I wrote it off as “me not un­der­stand­ing peo­ple” or “peo­ple are weird” for a sec­ond, like I usu­ally do, be­fore re­al­iz­ing that “bad at” re­ally means “lack­ing ba­sic knowl­edge”, which I had never re­al­ized be­fore.

And then I thought “I should ask some­one who is differ­ent from me why peo­ple do that, and even­tu­ally some­one will have an an­swer.”

But many peo­ple will have many more ques­tions like this. So, what have you ob­served peo­ple do­ing time and time again, but never un­der­stood? Or some­thing that you only un­der­stood af­ter a long time or ask­ing some­one about it?

And can Less Wrong tell us, not nec­es­sar­ily why (I for one can make up evolu­tion­ary psy­chol­ogy fairy tales all day if I want) but what con­scious thought pro­cess oc­curs be­hind these events?