Sure, but what if you tripped and sprained your ankle? Yeah it hurts in the moment, but would it cognitively impair you the next day? It certainly might; maybe when you're thinking about something while in the shower, you put too much weight on the ankle and the pain makes you drop your train of thought. I think the point that GP was going for was (or what I read at least) that there are many human experiences which cause some form of cognitive impairment; it's more important to see how deleterious the impairment actually is to the individual and to society before judging it.