I think that's a fascinating question. I once read an article that suggested that marriage be a 5 year contract that needs to be renewed each time it expires. I have wondered if this would cause people to take better care of their relationships - if they knew that their partner could just walk in 5 years. Ultimately, I think people know very little about how to be in a truly healthy, intimate relationship that can grow over time so making a lifelong commitment (especially now that we live 40 or 50 years longer than we used to) is more often than not about building a house of a lifetime on a foundation made of sand.