It's still magic even if you know how it's done.

It doesn't stop being magic just because you know how it works.

He had a notebook. He took notes in it. It was always useful. And them Sybil, gods bless her, had brought him this fifteen-function imp which did so many other things, although as far as he could see at least ten of its functions consisted of apologizing for its inefficiency in the other five.

Amazin'.' he said again. 'He just looks as though he's thinking, right?''Er...yes.''But he's not actually thinking?''Er...no.''So...he just gives the impression of thinking but really it's just a show?''Er...yes.'Just like everyone else, then really,' said Ridcully