Friedrich Nietzsche (1844-1900) was a famous philosopher who, despite descending into an irreparable madness, made many advancements in post-modernism as well as making some pretty inspirational yet controversial aphorisms.
In his Twilight of the Idols, Nietzsche writes in his eighth aphorism, “From the military school of life. That which does not kill me, makes me stronger.” Since then, his quote has been modified and has been accepted as, “That which does not kill us makes us stronger.”
Some, like me, consider Nietzsche an existentialist. My interpretation of this quote is as follows: Every obstacle, every struggle we overcome makes us who we are and adds to our wisdom. Whenever you face hardships, if you are able to knock them down and not let them hurt you, they make you stronger.