This book by George Spencer Brown had a profound impact on me.

In it the Author suggests that - and this is the explanation from Wikipedia (see the Links section) : 

The form (Chapter 1)

The symbol in drawing that looks like an angle, also called the "mark" or "cross", is the essential feature of the Laws of Form. In Spencer-Brown's inimitable and enigmatic fashion, the Mark symbolises the root of cognition, i.e., the dualistic Mark indicates the capability of differentiating a "this" from "everything else but this".
In LoF, a Cross denotes the drawing of a "distinction", and can be thought of as signifying the following, all at once:

  • The act of drawing a boundary around something, thus separating it from everything else;
  • That which becomes distinct from everything by drawing the boundary;
  • Crossing from one side of the boundary to the other.

All three ways imply an action on the part of the cognitive entity (e.g., person) making the distinction. As LoF puts it:

"The first command is:

  • Draw a distinction
    can well be expressed in such ways as:
  • Let there be a distinction,
  • Find a distinction,
  • See a distinction,
  • Describe a distinction,
  • Define a distinction,

Or:

Let a distinction be drawn". (LoF, Notes to chapter 2)
The counterpoint to the Marked state is the Unmarked state, which is simply nothing, the void, or the un-expressable infinite represented by a blank space. It is simply the absence of a Cross. No distinction has been made and nothing has been crossed. The Marked state and the void are the two primitive values of the Laws of Form.

The symbol can be seen as denoting the distinction between two states, one "considered as a symbol" and another not so considered. From this fact arises a curious resonance with some theories of consciousness and language. Paradoxically, the Form is at once Observer and Observed, and is also the creative act of making an observation. LoF (excluding back matter) closes with the words:

“...the first distinction, the Mark and the observer are not only interchangeable, but, in the form, identical".

To me, a great Light went on in my head! Basically, this suggests that nothing is real unless we make a distinction, where we distinguish something from nothing (or everything in philosphical terms). Brilliant. This explains how we build up our view of the world in our heads and as such everybody draws the distinctions differently, because each one of is different in time and space. Again, brilliant!

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