Comments and Expansion
The most important part of this practice is to grow confident in how thoughts themselves, whatever their content, unravel, and vanish
Thoughts do this, and everything else too. From the life cycle of a quantum particle to life in the universe. And in between, each thought and emotion showing up in awareness for some moments. That is impermanence, "anicca".
It's a reason to consider the preciousness of each moment, and of life.
It's also a reason to be courageous when "sitting in the fire of one's emotion" rather than being overly reactive: there's a certainty that "that too shall pass". Even strong negative emotions only last moments.
Meditating on impermanence, "anicca", is one of the three main "liberating ways of looking" identified by Rob Burbea in "Seeing That Frees: Meditations on Emptiness and Dependent Arising" (Burbea, 2015).
All phenomena can be seen to be impermanent (anicca), unsatisfactory (dukkha), and not-self (anattā). There are many ways to look at impermanence. One can meditate on impermanent micro-structures such as an individual emotion as it evolves moment by moment , or on "the fleeting world" at large, as in the beautiful poem from the Diamond Sutra
"Thus should you think of all this fleeting world: Like a drop of dew, or like a star at dawn; A bubble in a stream, a flash of lightning In a summer cloud, A flickering lamp, a phantom, and a dream"…quoted in (Burbea, 2015, p. 157)
In the end, death is the big metaphor for impermanence.
So, when I recently saw this book-title, I wondered about how that promise should come true
Burbea, R. (2015). Seeing That Frees: Meditations on Emptiness and Dependent Arising (English Edition) [E-book]. Hermes Amāra. https://www.amazon.de/dp/B00SI7PQD8
This book is praised by Michael Taft, one of the best contemporary teachers, in is "Best meditation books of 2020" https://deconstructingyourself.com/best-meditation-books-2020.html