A person's actual level of intelligence is not static, it varies from moment to moment, depending on their level of wakefulness, what they had to eat that day, their momentary emotional state, and a hundred other factors. The "smartest" person you know can still step into a rake and that absolute dumbass who just cut you off in traffic might actually have a very good reason for what they are doing. I chalk up the whole enterprise of intelligence measurement to yet another instance of where we individualize something that depends as much on externalities as not.