Coming to the Realisation of why you Focus on the Breath in Meditation

In meditation, you do not consciously breath but simply observe it.  You observe your breath as an anchor to return to it whenever your mind wanders.

With time that simple observation makes you realise you are not your breath.

At the moment you realise that you are not your breath - you become aware of the breath, and aware that you are breathing.

That you are not your body but become aware of your body. 

You suddenly realise that you are aware you become aware of your awareness.  You come to the realisation that you are "awareness".