Humans will replace using their brain with just asking AI for answers, first starting in school so that they don't learn anything or develop the habit of thinking and then in their adult lives so that they can't function without an expensive AI subscription. Eventually nearly everyone will be unable to blow their nose without consulting a LLM for instructions.

Even if you're aware of this and try to use AI in ways that don't compromise your intellect, you won't be able to escape the trap. It's just too powerful, too much of a productivity amplifier, just plain too convenient to avoid entirely and so you'll sink deeper and deeper into the quagmire as your mental skills devolve into mush from disuse, all while insisting to yourself that you're just as sharp as you once were. Thus AI succeeds in destroying humanity without even having to reach sapience itself.