Many times players and GM's ignore, change or get a rule wrong.  Sometime by accident, other times on purpose because  they don't like that rule.  Known as "House Rules", "Home Rules", and many other names changing and omitting rules is done all the time.   There are some type of rules that usually go out the window, whether you play the "Best Selling RPG" or the smallest "Indie RPG ruleset", rules get ignored.