That tough boss, that job that drove/drives you crazy, that bad relationship or rough breakup, it does a lot more for you than when you're just coasting.
We don't like to think about life this way, that it's the difficult experiences that train and shape us. Hardship, mistakes, discomfort, all of it feels awful at the time and of course we can let it embitter us and make us unhappy and cynical. But hopefully we also use the opportunity of difficulty to achieve growth.
Feeling good never requires us to change. Feeling good can be the result of changing. We need the catalyst of difficulty to provoke introspection, to see how we're contributing to out own dilemmas and to learn how to avoid repeating our mistakes.
In "The Mastery of Love," Don Miquel Ruiz writes that we let people treat us only as badly as we treat ourselves. When we learn to love ourselves, to really care for ourselves, we naturally surround ourselves with other people who treat us well. We just don't have a tolerance for abuse. But sometimes it takes some external hardship before we realize how to be gentle with ourselves.