It's almost hard to imagine life before headphones and customized playlists, a time when you couldn't take your favorite tunes with you no matter where you were going or what you were doing. That was the case, however, for every single person who lived out their lives prior to the late 1970s.
Before then, music was a destination activity. In the distant past it was something you either had to make yourself or else listen to live, in person, and perhaps never hear again. Later, music began being recorded but was still tethered to a destination. In order to listen you had to be in the car, at a venue, or near bulky audio equipment at home. Listening to music was necessarily communal. People had to agree on what to listen to and kids everywhere had no choice but to scoff at the dated musical tastes of their parents.
The invention of the Sony Walkman in 1979 changed all that (via Design Museum). By combining a couple of existing technologies in a novel way, people could take their music with them wherever they went and listen to it privately for the first time in history.