@NutterflyEffect
Well no because lots of people on this thread disagree with you *@kindaclassy*, and as I said people with ASD or anxiety would struggle with unwritten rules, so it can be that hard. And of course social etiquette changes! 50 years ago for example a woman couldn't ask a man out, 100 years ago she couldn't show her ankles. Social etiquette changes as we move with the times
people on this forum also disagree about replying to RSVPs, turning up uninvited, turning up without replying or despite replying no...
Just because some posters refuse to bother themselves with basic manners, it doesn't mean they will suddenly disappear.
It's not even an unwritten rule, this is the very first link when you google it, but you will find plenty more.
Usually, such dinners are preceded by cocktails lasting from half an hour to an hour. This gives all the guests the chance to arrive, catch their breaths, have a drink, and meet or greet the rest of the party. A polite guest arrives within a half an hour of the stated start time. If you are running late or cannot arrive within the first half hour, warn your hosts in advance.
This one is the second link in google:
Don’t arrive on time to a dinner party
While you might think that arriving on time is a punctual courtesy, it’s actually considered a little rude. “A thoughtful guest will arrive exactly 10 minutes after the start time,” Musson says, “and arriving early is unacceptable; your host may still be getting ready.”
It's also a common jokes in books, movies etc..
It's disingenuous to pretend you have to be a mind reader to know the basics. Now if people make their own rules, you can't guess them. If you invite people for 7pm and serve food at 7.01, they will be caught unaware if you don't warn them!