Suppose your friend has a bag of M&Ms. She is counting each color separately. You have five orange M&Ms, and you add them to her mix. But this stops her being able to count them properly. She wants you to remove your five orange M&Ms from the six orange M&Ms that she has. But they are now mixed. How do you know which were the original M&Ms and which were the ones you added?
Source: Creation Moments