I take a very philosophical view of marriages and personal relationships. I will say up front, I do not like the word "failure" applied to relationships. That word implies someone failed.
People change over time, situations change, things occur, wants and needs change, and when that happens, it's sometimes best to have things end and move on. It's not a failure, though. Things change, that's all.
Did the people involved learn something? Have some good experiences? Even if it ended, doesn't sound like failure to me, just a learning experience.