A friend of mine sent me a link to a YouTube video from a show that he watches called Mad Men. It was a clip from an episode called The Wheel and it was quite touching. Here is the meat of the quote that I found online:
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 are loved.
Considering our memories as sort of a time machine, is completely apropos. When we are reflecting on our pasts, we are catapulted into it. Sometimes it is the way a sunbeam crosses the trees or a song, maybe even a smell, that stimulates memories. Once they are stirred, we have to revisit those experiences whether they are delightful or painful to recall.