What percentage of relationships are successful?

I qualify a successful relationship is one that doesn't end for bad reasons. If you relationship ended due to distance, life goals, lifestyles, etc. then it didn't end for bad reasons. The relationship wouldn't have ended except for that thing. Granted you can't know if your current relationship is successful, but you can probably rank it compared to others to get a rough idea. How many relationships are actually successful?

What percentage of relationships are successful?
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