In the restaurant/buffet analogies above, one could add that there might be something you want that isn't on the menu. In which case, you can ask for it and you'll likely get it but you might have to wait for someone to go out and get the ingredients, then prepare it. And whilst vegetarianism, veganism, nut allergies and most other diets are catered for, there will always be people with unusual dietary requirements that want something else.