I was creating a custom game world for Pathfinder 1e. My roommate helped me compile all the rules changes and made a PDF for them, with full art and all my descriptions of the unique races and rules, it looked very professional and easy to read.
I gave the pdf to all my players to read.
Day One: "Uh, why are there no Ninjas?"
"The area of the game you'll be playing with has no real contact with cultures that are anything like Japan or Asia, so I felt there was no reason to have Ninjas or Samurai."
"You could have Ninjas, just call them something else."
"I could have, but I didn't."
"Whatever."
Day Two: "Hey! No Paladins?!"
"I'm tired of all the arguments about Paladin restrictions limiting roleplay, and I honestly don't want to feel like I need to step in and dictate how you play your character. The fact that the Paladin has built-in restrictions on behavior that I then have to enforce is then self-defeating."
"But I want to play a Paladin!"
"You can play a Cleric and be a soldier for your God. Or Good."
"But I wouldn't be able to Smite."
"Take the Destruction Domain."
"Couldn't you just let me play a Paladin without the restrictions?"
Day Three: "Hey! No Dwarves?!"
"They exist in the setting, but won't be encountered in the starting area."
"So I can play a Dwarf then, I'd just be the only one?"
"No. I want to keep Dwarves a secret for now."
"Could I be a Dwarf with amnesia?"
"AUGGH!"