The famous quote "That which does not kill us makes us stronger" was authored by the German philosopher Friedrich Nietzsche. This thought reinforces the idea that overcoming hardship or adversity can lead to greater strength and resilience. Nietzsche first expressed this idea in his book "Twilight of the Idols," published in 1888. His philosophy often emphasizes personal growth through struggle and reflects a broader existential approach to understanding human experience and vitality.