"First, if something doesn't exist, then it doesn't exist, but whatever does exist is composite and not a single, indivisible entity. All things are made up of various ingredients and these ingredients form existing things.

Therefore, all phenomena that exist are composed of various ingredients and as a result are impermanent. Living beings die, objects wear out and disintegrate. At this coarse or obvious level of impermanence, everything changes over time, and this is obvious and can be understood by everyone. The subtle level of impermanence is the main concern here; it is the momentary impermanence of every instant.

When looking at momentary impermanence on a gross level, we can see that a person changes from childhood to adulthood.

One may think that there is continuity in the change that takes place. One may wonder when this change takes place and conclude that every year, everybody is different. However, a change doesn't automatically take place at a certain point each year.

One may conclude that every month, everybody is different, but the change doesn't automatically take place at a certain point in each month either.

One may conclude that every day or every hour, everybody changes. We follow this reasoning down to every single instant in which a change takes place, so there is impermanence in every instant.

This is the subtle level of impermanence. It is easy to see changes that take place over the years, but, in fact, changes are taking place in every instant.

[...]

Whatever phenomena we can perceive are empty like water bubbles. Although we can hear and see things, nothing has a true reality in itself; there is no true self in the individual and no true existence of phenomena. In spite of the fact that they appear, phenomena have no substantial or true reality of their own. Thus it is said that all phenomena are empty and have no self."

Thrangu Rinpoche