Mono no aware is a Japanese term for the awareness of impermanence (mujō 無常), or transience of things, and both a transient gentle sadness (or wistfulness) at their passing as well as a longer, deeper gentle sadness about this state being the reality of life.  Impermanence is the philosophical problem of change. In Buddhism, the three marks of existence are 3 characteristics of all existence and being namely: Impermanence (anicca), non-self (anatta), and unsatisfactoriness or suffering (dukkha).

When the heart weeps for what it has lost, the soul laughs for what it has found. ~ Sufi aphorism

The Greek philosopher Heraclitus shared the same sentiment that nothing in this world is constant except change and becoming (Everything is impermanent).