Most successes are unhappy. That's why they are successes - they have to reassure themselves about themselves by achieving something that the world will notice.
I think the person who has had more experience of hardships can stand more firmly in the face of problems than the person who has never experienced suffering. From this angle then, some suffering can be a good lesson for life.
Dear little Swallow,’ said the Prince, ‘you tell me of marvelous things, but more marvelous than anything is the suffering of men and of women. There is no Mystery so great as Misery.