What does it mean to have a successful relationship?

All relationships end sooner or later. Is a successful relationship one that doesn’t end until death? Can you have a successful relationship that does end before that point, or an unsuccessful one that doesn’t?

I have my own ideas about the answers to these questions, but I’m interested in hearing what you all think. I’d also love to hear stories about relationships that you consider a success, whether they were your own or someone else’s.