Terry Pratchett, bestselling fantasy author and creator of the Discworld series, in Thief of Time:
For something to exist, it has to be observed.
For something to exist, it has to have a position in time and space.
And this explains why nine-tenths of the mass of the universe is unaccounted for.
Nine-tenths of the universe is the knowledge of the position and direction of everything in the other tenth. Every atom has its biography, every star its file, every chemical exchange its equivalent of the inspector with a clipboard. It is unaccounted for because it is doing the accounting for the rest of it, and you cannot see the back of your own head.
Nine-tenths of the universe, in fact, is paperwork.