Bhagavad Gita · Chapter 2: The Path of Understanding

Bhagavad Gita 2.27

jātasya hi dhruvo mṛtyurdhruvaṃ janma mṛtasya ca | tasmādaparihārye'rthe na tvaṃ śocitumarhasi ||

For death is certain for one who is born, and birth is certain for one who has died. So you should not grieve over what cannot be avoided.

Modern context

Whoever is born will die. It is the one certainty of life and the one we most avoid looking at. Krishna is not saying that loss should not hurt. He is saying that to fight against what cannot be otherwise only adds a second suffering to the first. Accepting the unavoidable frees our energy for what can be changed.