That's true enough - you don't want to reference something in the discussion that you planned to put in the introduction, then forget to put it in the introduction
Same goes for fiction. Nothing wrong with writing out of order, as long as you join up the dots
Bear in mind it might make things harder (or at least, more work for you) if you decide to change something, since you've already written what comes after.
So, do what you want
This wouldn't work for me - I enjoy driving myself towards those "special" scenes. If the shoe fits, etc.