We live as if everything around us is forever: pain, fear, stubborn hold on success or a person who is afraid to let go. But everything passes. What seems like the end of the world today will be just a memory tomorrow.
The Buddha compared life to dew on the grass and a flash of lightning - not diminishing its value, but reminding us of its fragility. Nothing lasts forever, so it's foolish to let temporary things rule us.
Leave what is gone. Appreciate what you have. And don't put off life for later.