Consolations

Have you ever noticed that a popular phrase for consolement is "There, there." i.e. You dropped your ice cream and your mom says, "There, there, I'll get you another one..." What does this phrase mean exactly? It seems to stipulate that by pointing out something seemingly nonexistent, not once, but twice, you can make a person feel better. Or perhaps it's "They're there.", in which case, who is it, and where are they? And why is this supposed to make me feel better?