What we have here is rather someone ‘acting as if they were stupid’. It’s not just that they failed to apply the concept of betrayal, but that they literally didn’t think of it: it was effectively ‘offline’, due to emotional and other pressures. In this kind of case, agents possess the necessary intellectual tools but unwittingly lock them away. This marks an important contrast with dumbness – we can make ourselves stupid, but we don’t make ourselves dumb.

This is a good insight. Lots of stupidity is a lack of imagination rather than a lack of raw intelligence.

This is also an idea that Julia Galef illuminates in great detail in her book "The Scout Mindset." She describes this as the difference between "Scout Mindset", which attempts to figure out what is correct, and "Soldier Mindset", or "stupidity" the way this article describes it, which attempts to fight to confirm what one already believes to be true.