This article explores the Japanese concept of natsukashii: a Japanese word used when something evokes a fond memory from your past. It's a word you exclaim as a smile creeps across your face. For instance, when you hear a song you loved as a teenager, or when you come across an old train ticket stub in your pocket. In some cultures, nostalgia is often full of sadness. But natsukashii - which derives from the verb "natsuku", which means "to keep close and become fond of" - indicates joy and gratitude for the past rather than a desire to return to it. In Japan, natsukashii is a reminder that you are fortunate to have had the experiences you've had in life. The fact that you cannot return to those experiences makes them all the more poignant.