I disagree with your sentiment, and think the examples work. If your aim was to run a coffee shop forever and you quit, then yes you have failed. If, on the other hand, your aim is to enjoy and have the experience of running a coffee shop, then doing so for two years and stopping is a success. Similarly with a relationship. You can have succeeded in having a mutually fulfilling relationship that you both have happy memories from, even if you then grow apart. It succeeded in its aims of spending time enjoying being a relationship.