Nostalgia

"Nostalgia - it's delicate, but potent. Teddy told me that in Greek, 'nostalgia' literally means 'the pain from an old wound.' It's a twinge in your heart far more powerful than memory alone. This device isn't a spaceship, it's a time machine. It goes backwards, and forwards... it takes us to a place where we ache to go again. It's not called the wheel, it's called the carousel. It let's us travel the way a child travels - around and around, and back home again, to a place where we know we are loved."
-Mad Men episode 113, "The Wheel"