My favorite analogy for this, and the one that really made me 'get it', was posted on Reddit a number of years ago, and was something to the effect of:

Imagine you're sitting around the dinner table with your family, and your dad is passing around a bowl of mashed potatoes. However, instead of handing it to you, it gets passed right by you to your sister. And you speak up and say, "I should get some, too!" Your dad looks at you and says, "Everyone should get some," and the family continues passing the bowl around as before. And you're thinking, yes, that's true - everyone should get some, but only one of us is not getting any right now and pointing out that everyone should get some doesn't make me any less hungry.