I recently came across this post, which challenges readers to propose a definition for rationality. The post is several years old so I’m clearly late to the game, and I’m sure that most everything has been said already, but I figured I’d take a crack at it anyways.
I think my 'rational' model of devotion to rationality is to distinguish between 'full spectrum style' and 'partial spectrum' style experiences. In a full spectrum style experience, you encounter enough of the space you are interacting with to notice both the presence and absence of things (i.e. this is partially true of vision, you see both what is there and what isn't, or with a flashlight you see both the lighted portion and the darkened portion). With a partial spectrum experience you only experience what is present and have to deduce what is absent (i.e. you only hear the sounds that are actually happening and it takes training or experience to pick out the sounds that are missing). My guess is that the experience of knowing things is partial spectrum, that you are directly aware of your 'knowledge' but not aware of what you don't know, which systematically prejudices people to weight their knowledge whenever they are doing reflection about knowledge.
Or to adopt a traditional explanation "their thinking became futile and their foolish hearts were darkened. Although they claimed to be wise, they became fools" (Romans 1:21b-22a).