We say "Was mich nicht umbringt, macht mich stark." (“What doesn't kill me makes me strong."). I also found the variants:
"Was mich nicht umbringt, macht mich stärker." ("stronger")
"Was dich nicht umbringt, macht dich stark." ("you").

I understand this as self-encouragement in a situation that threatens to overwhelm me. However, this can also be expressed in a self-pitying, complaining manner. When you feel that someone or ‘the fate’ demands something of you that you consider unfair, and you then utter the phrase, you distance yourself from the saying, you reject it.
If you don't apply the saying to yourself, but use it against someone else, it can take on a different meaning, namely a call to persevere, to not “make such a fuss.”

The saying is attributed to Friedrich Nietzsche (Götzen-Dämmerung oder Wie man mit dem Hammer philosophiert, chapter Sprüche und Pfeile, § 8).
http://www.zeno.org/Philosophie/M/Nietzsche,+Friedrich/Götzen-Dämmerung

This saying is sometimes used in a manipulative way. The generation of parents who had experienced the World War II, liked to use this saying with the intention of teaching their children to be hardy. They lived according to the motto “what makes you strong is good.”

Nowadays, this saying is associated with “resilience”, it is said to clearly express what is meant by “resilience”. Until recently, I have hardly come across the term "resilience". Now, since the society, the people shall be made kriegstüchtig, is it is being used almost inflationarily.

Edit:
Follows an example for the phiöosophy that sometimes lies behind the phrase:
"A young employee calls the office in the morning: 'I think I'm coming down with something, I won't be coming in today.' When a baby boomer—the oldest generation currently in the workforce—hears this, they are speechless. It's obvious: young people are lazy, work-shy, and soft. Baby boomers are trained in perseverance. 'What doesn't kill me makes me stronger' was often enough their motto. To this day, they come to work with fever and pounding headaches, showing great loyalty. From the perspective of the younger generations Y and Z, this is almost childish: 'They are unable to perform properly for days, infect the whole team, and are still proud of their work ethic! Instead of taking a day off to recover.'" (translated by DeepL)
https://www.carelink.ch/de/jede-generation-tickt-anders-und-nun/

Phrases and sayings from all over the world