I always thought this was simpler than people often make it seem.
Other philosophies say there is someone behind experience, experiencing, for example, in western philosophy, homunculus theory. Buddhism says there is just experience, so you could say experience is self.
But experience doesn't fit any traditional definition of self or even any traditional definition of a concept or compounded object - it lacks an unchanging nature. There's nothing you can say about it to describe it - you can describe an experience using terms relative to other experiences, but you cannot describe experience itself, which is why it is unconditioned. When the lack of an experiencer is realised, attention given to attempts to improve the condition of the experiencer fades and all attention is given to experience. Life becomes luminous, blissful and so on.
Of course, experience always was all there was, but illusorily in a kind of feedback loop or cycle of samsara. This is where words, or at least my words fail in explaining. Where did the arrow come from? Can't be answered and a mistake to try, I guess.
Supposing the idea of an unchanging nature is a category mistake in the first place. The words 'unchanging nature' are just words, they lack an objective correlate.
Oh dear, have I made this simpler, as I claim at the beginning, or more complex?
Not twice, not three times, not once,
the wheel is turning.