The biggest mystery in the universe is you.
– Adyashanti
What a thought tells us we are is not what we are. Reality is always more than and different from any thought.
Even within direct noticing, there is always more to discover.
Since to us, the world happens within and as what we are, any mystery is the mystery of ourselves.
Adya is using this as a medicine for our tendency to think we know, whether we assume we know based on what a thought tells us or our more immediate noticing.
That anything is at all, is perhaps the greatest mystery of all.