Since CD players included a shuffle button. Before that, since it was possible to record songs from the radio into a blank cassette. And before that, since DJs

Since CD players included a shuffle button. Before that, since it was possible to record songs from the radio into a blank cassette. And before that, since DJs included a second turntable to allow them to structure a set their way (Jimmy Saville pioneered this. Such a shame he turned out to be a monster).