If you have that gnawing feeling that you’re forgetting something, chances are you’re right. And it may not be your keys, but something a little bigger. César Hidalgo, director of MIT’s Collective Learning Group, explains how society experiences generational forgetting.

Hidalgo says: even if you have a pristine memory, time greatly impacts the names, books, movies, and historical events that are common knowledge at any given moment. Researching how culture gets passed down (or doesn’t) from generation to generation can tell us more about why some famous people stay relevant, while others seem to fade away.