In the comments of my last post, Pied Cow asked why anybody would want to treat misfortune and good fortune in the same way. It's a fair question, since we intuitively feel that grieving and celebrating are natural. However, consider the kind of person who suffers misfortune far more often than good fortune, and ask yourself whether that kind of person might find comfort in Stoicism. Two quotes, now - the first from Schopenhauer and the second from Marcus Aurelius:
A quick test of the assertion that enjoyment outweighs pain in this
world, or that they are at any rate balanced, would be to compare the
feelings of an animal engaged in eating another with those of the animal
If thou art pained by any external thing, it is not this that
disturbs thee, but thy own judgment about it. And it is in thy power to
wipe out this judgment now.
I hope this goes some way towards answering that question.