James Mal has proposed an OD&D gameplay principle: D&D is always right. In other words, if you find an apparent contradiction or nonsensical rule, give it the benefit of the doubt and restructure your gameplay expectations to justify it. I think of this as similar to the fandom practice of creating explanations for apparent errors: for instance, if Star Wars is Always Right, you get to come up with a fun explanation for why the Millenium Falcon can do the Kessel Run in 12 parsecs.
This can be a fun practice, and often leads to interesting and quirky world details that make it seem like a living place.
Here’s another principle: Ceremony is Always Right.
Real old-time superstitions, rituals, and beliefs about magic should be a great source for worldbuilding quirkiness. Assume that any ceremony or ritual is not just ignorant superstition, but has a part in making the world the way it is.
I talked about funeral practices being necessary for speeding souls on their way. The same priests who do funerals probably do weddings too.
weddings in D&D
A wedding’s main function is for legitimizing heirs, right, for inheritance? Besides the legal penalties, what is the magical significance of being born out of wedlock?
I think medieval bastards were perceived as chaotic force. They have no claim on the lifestyle they’re born to. If they want to get anything, they need to upset the social order to get it, like Edmund in King Lear. What if bastard babies have a chance of being possessed by a demon, or being swapped for a changeling or something? A demon-possessed or changeling child will grow up with the goal of disrupting the family, either by seizing power or just killing everybody.
In ancient days, when demons ruled, demon spirits possessed maybe one in 10 children. The wedding ritual, which protects the children of a marriage, was one of the turning points in the war against the demons.