It is a trust issue. You don't trust that your marriage will work out. Because others marriages have failed.
People in NY didn't believe their houses could/would ever be flooded which is why they didn't have flood insurance but Sandy came through and flooded their buildings. Even things that don't seem likely can happen.
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Why did u totally ignore everything I said and then try to put words in my mouth 
Whether those changes bring a couple closer together or have them drift apart is another issue, but change itself is unavoidable, especially over the course of a decade or two.

