What is the essence of 'I'?

The essense of I is a reference to yourself, yourself having a relative defenition, its essentially everything you cant explain, for instance; Space is to complex to understand, yet we still have a name for it. This name is the only tangible part of I, it references yourself, in a short amount of time so that sentence structure can be maintained fluidly. I is a variable, its kind of funny that it happens to be one letter long like most variables in math that represent larger more unknown numbers.