In all my years,  I've heard only a handful of people say, "What doesn't **** you makes you stronger."

It might be because it's only half true.

It might be better to say, “What doesn't **** you makes you harder."

What doesn't **** you makes you harder:
-to tear down
-to betray
-to lie to
-to leave
-to forget

But it's a two-sided coin.

What doesn't **** you makes you harder:
-to get to know
-to trust
-to understand
-to get close to
-to remember

Don't be a wall, be a sea, for walls can be torn down, by raindrops alone,  and water is the strongest force on earth, yet gentle to the touch.