"Epictetus presents us with the image of Zeus as an athletic coach: ‘It is difficulties that show what men are. Consequently, when a difficulty befalls, remember that God, like a physical trainer, has matched you with a rugged young man.’ Why do this? To toughen and strengthen you, so you can become ‘an Olympic victor’ — in other words, so you can have the best life possible. Seneca, by the way, argued along similar lines: God, he said, ‘does not make a spoiled pet of a good man. He tests him, hardens him, and fits him for his own service.’ In particular, the adversities we experience count as ‘mere training,’ and ‘those things which we all shudder and tremble at are for the good of the persons themselves to whom they come’."
— William B Irvine, A Guide to the Good Life: The Ancient Art of Stoic Joy