In the intense but very important book Man’s Search for Meaning, psychologist Viktor Frankl suggests that a key factor to human mental wellbeing is a sense of meaning. There are all kinds of ways to find meaning in life, but if you’ve got nothing else, you can still find meaning in suffering.
This is the idea behind the it’s for the best exercise. It takes something you’re not happy about and challenges your brain to extract meaning from it. It’s possible to do it with suffering at any level, past, present or future.
The only hard part is making your mind flexible enough to see the meaning in things which would otherwise be very painful. But that’s just a matter of practice and perspective. Start with small, harmless suffering and let it become a habit. Let your ability to find meaning get stronger and stronger.