With marriage it might just be a practical thing; for instance if you have wildly different ideas of "what is acceptable food" then it might be really hard to eat together, and eating together is a huge party of how we are social.

And some choices aren't really about being "right" at all, but just being about "what I like doing". I spent my weekend climbing Welsh mountains, which I think is fun *for me* but it's not fun for everyone. I think it's hard to tell when someone has made a choice because they think it is the One True Way and when it is because they think it is the Fun Way For Them.