Things are often under your nose, but you don't see them because they are at unusual angles or not how you left them when you last saw them, whatever they are: a pair of glasses, a tube of toothpaste, even your mobile phone.

The reverse principle of perception--or misperception--occurs when an elemental or non-human entity is standing right next to you. You don't see it because:

--you are not looking for its correct appearance
--you are not expecting to see it
--you are psychologically blind to it because you have never seen anything like it before, and so your psyche does not allow it to register in your mind.