You are an afterthought.
(The explanation below may seem redundant, but sometimes redundancy is useful.)
Every moment is gone – no longer is – before the mind can process what was experienced in that moment. The mind cannot experience anything other than what was experienced. All thoughts (including thoughts of you, as the experiencer) are afterthoughts. All that the mind is capable of being aware of – thoughts of, mental interpretations about, memories (both immediate and long-term) and stories of – is history. (Or fantasy about the future, which is entirely based on thoughts generated by perceptions, mental interpretations, memories, and stories of the past: history).
That which experiences has no thought of what is experienced.
All thought of what is experienced is afterthought. And this afterthought is done by the you that thinks it is the experiencer.
But thought comes after experiencing happens. Experiencing happens in the moment experiencing happens. Thought (about any experience) happens after experiencing happens. The thinker is not experiencing in the moment… the thinker is thinking about experiencing that happened in the past. (No matter how quickly this appears to transpire.)
So… who, or what, is experiencing when experiencing happens?
That is not an afterthought – and no thought about it, is it.