You don’t miss the water until the well runs dry.

You don’t miss the water until the well runs dry.

you never miss the water till the well runs dry
It is only when someone or something is gone that we truly appreciate them or it.

I was in such a rush to start a career and become an adult, but now all I want is the carefree life I had when I was in college! You never miss the water till the well runs dry, huh? I should have made a greater effort to show Janet just how much she meant to me, but you never miss the water till the well runs dry. Now she's married and living on the other side of the planet.

(TFD)