Flow
The world of phenomena is flow, always in flux, always new, different, fresh.
To the extent abstractions are recognized as abstractions, as just a part of the landscape, this freshness is experienced immediately and directly. And to the extent abstractions are believed in, there is a sense of something fixed. This is where boredom comes in as well - we tell ourselves "this is exactly the same as ...", believe in it, and by necessity experience boredom.
We see through abstractions as just abstractions, in one area after another, and experience this freshness more and more. Until the final idea is seen through, the idea of "I" as a segment of what is, and now - the freshness of the world of phenomena is indisputable. There is no "I" to resist the flow. The world is always new, fresh, different.
This flow shows up in many ways. One is in our experiences of the present as always fresh. And another aspect of it is in the flow of experiences themselves. There is all sorts of things coming up from and through our human self - sensations, feelings, emotions, thoughts and views and so on, and they come and go on their own. None of them seems to stick around for very long. They happen within and as the groundless ground, and then are gone again and something else comes up.
Flow and sincerity
Just from my own very limited experience of this, I see how confusing this can be for other people. Something comes up and is expressed, whether it is an emotion or a particular view, and then others expect that emotion or view to stick around. And it often doesn't.
It was very much alive as it was expressed, and then is gone. And something else comes up and is alive.
From a conventional view, being authentic is often seen as being consistent. To hold onto emotions for a while and in particular to hold onto specific views. But as we deepen into realization and familiarity with the natural flow of the world of phenomena, authenticity is just sincerity about what is alive right now. And it is always new, different, fresh.
This sincerity embraces what is alive right now, including the idea of what used to be alive - the memory of it. So this gives it some appearance of continuity and consistency for others.