I find that discussing an idea out loud is often the way to kill it stone dead.

Potter is mocked by a faculty member for the idea that there is evil in the world from which even children need to learn to defend themselves by the actual practice of doing so rather than familiarity with theory.

I just wondered where you —” Ron broke off, shrugging. “Nothing. I’m going back to bed.” “Just thought you’d come nosing around, did you?” Harry shouted. He knew that Ron had no idea what he’d walked in on, knew he hadn’t done it on purpose, but he didn’t care — at this moment he hated everything about Ron, right down to the several inches of bare ankle showing beneath his pajama trousers.

And the idea of just wandering off to a cafe with a notebook and writing and seeing where that takes me for awhile is just bliss.

Tell me, how is Lucius Malfoy these days? I expect he's delighted his lapdog's working at Hogwarts, isn't he?" "Speaking of dogs," said Snape softly, "did you know that Lucius Malfoy recognized you last time you risked a little jaunt outside? Clever idea, Black, getting yourself seen on a safe station platform. Gave you a cast-iron excuse not to leave your hidey-hole in future, didn't it?

I have gone temporarily deaf and haven't any idea what you said, Harry.

The idea of a teenage Dumbledore was simply odd, like trying to imagine a stupid Hermione or a friendly Blast-Ended Skrewt.

but the idea of the Dark Lord in possesion of the Deathstick is, I must admit, formidable.

The poor are discussed as this homogeneous mash, like porridge. The idea that they might be individuals, and be where they are for very different, diverse reasons, again seems to escape some people.