Imagine you have a group students and a set of rules for the school. Instead of posting the rules in a common place all the students must reference you hand each one a copy of the rules. Each student is told they must follow their copy of the rules to the letter.

Now modify one of the rules saying that in the case of a disaster you should go to the new disaster shelter. You have to go to each student and modify their set of rules. If one of the students gets missed and a tornado hits the student will go to the old place and die a horrible death.