Often attributed to Dr. Seuss without citation; also cited as an anonymous proverb.
Don't cry because it's over. Smile because it happened.
Notes from Wikiquote
This quote has also been attributed to Gabriel García Márquez, in Spanish: "No llores porque ya se terminó, sonríe porque sucedió." | Compare lines from In Memoriam A.H.H. of Tennyson:
'Tis better to have loved and lost
Than never to have loved at all.