You are the awareness watching your thoughts, not the thoughts
Singer opens with a question designed to jolt readers out of autopilot: notice that you can hear the voice in your head talking. Who is doing the hearing? That observing presence — the one aware of the thought, rather than the thought itself — is, in his framework, your actual self, which he sometimes calls simply "awareness" or "the witness."
He points out that we routinely say things like "I need to make up my mind," language that implicitly separates the speaker from the mind being addressed, revealing an intuitive sense that we already have of this distinction, even though we rarely act on it.
Once this becomes experientially real rather than just conceptually understood, the mental chatter stops feeling like an inescapable core identity and starts feeling more like weather passing through a sky that was never actually disturbed by it — the sky being the awareness that simply watches, unaffected underneath.
Takeaway: throughout the day, briefly ask "who is aware of this thought right now?" — the shift from thinking to noticing is the whole practice in miniature.