Rudolf Steiner: "Those who have known pain and suffering will always say that while they are happy to accept joys and pleasures, they would not want to do without pain and suffering. We owe all our wisdom to pain and suffering in past lives on Earth. A countenance which reflects wisdom in this life does so because it has been sentient in earlier lives of the pain that is cosmic cohesion."
Source: June 20, 1907. GA 100. "Theosophy and Rosicrucianism," lecture 5. In True Knowledge of the Christ, p. 41
a different translation: https://martyrion.blogspot.com/2021/07/our-life-between-death-and-rebirth.html