Having a reflex to think about a question fast enough compared to the reflex to rationalize can cause someone to not notice their arguments for some answer, then say they never rationalize, or just not rationalize.
I have had periods in my life where I would have been convinced I was thinking absolutely clearly, but in retrospect it was blitheringly obvious that I was rationalising like hell.
People's subjective reports turn out to be unreliable, news at 11.
Anna Salamon and I are confused. Both of us notice ourselves rationalizing on pretty much a daily basis and have to apply techniques like the Litany of Tarski pretty regularly. But in several of our test sessions for teaching rationality, a handful of people report never rationalizing and seem to have little clue what Tarski is for. They don't relate to any examples we give, whether fictitious or actual personal examples from our lives. Some of these people show signs of being rather high-level rationalists overall, although some don't.