Image source

Example sentences from the web:

• John: Hey! I wanted a glass of milk too!
  Sarah: It’s too late. You snooze, you lose.
• Isabel: Mark is so selfish, he knew I wanted to go to the show, but yesterday he bought the last ticket for himself.
  Cristina: If it was so important, why didn’t you buy the ticket before? You snooze, you lose.

Image source