Unknowing.

Sometimes, I miss that feeling you get when you meet someone new or move into a new place, or experience something you have never seen/done before.
It's the kind of thing that you can not create or reproduce.
Similar to when you stop believing in Santa Claus - you try so hard to hold onto the childhood image, and to make yourself believe it again.
But once you know something to be true, you can not recreate the feeling of unknowing. It is impossible to bring yourself to understand why you thought differently before.