system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it that certain word associations just have a single way that sounds "right."

For example, if I tell someone to fetch me some pepper and to get the salt as well, I'll never say that. It's "Salt and Pepper." Not "Pepper and Salt." Just "Salt and Pepper." Then you have "Nieces and Nephews," "Ladies and Gentlemen" (Though that seems to be more of a phrase), "Fruits and Vegetables," etc. There's obviously many more, but I can't think of them at the top of my head.
gpt
Because these are commonly used combinations and the more you hear it the easier it sticks to your brain. Its a historical accident that we use "Salt and Pepper" instead of "Pepper and salt." If half of america used "Salt and Pepper" and the other half "Pepper and salt." eventually one of them would win over the other, because it represents an unstable equilibrium, the more people which use one, the more influence that will have to get even more people to use it.