I've been making them in some form or another since I was 13 and got a "boombox" that had two tape decks, so I could record from tape to tape, CD to tape, radio to tape, or microphone to tape. The form that shifted over the years, but the idea of making mixtapes of some sort has been there a long time. Some I just add to as I come across or think of songs, or if I get a new idea I just create one (a couple of my recent threads have related to versions of them). It's just an ongoing thing, it's not like it was all created at once. Same way someone builds any sort of collection, just that these are more of virtual compilations of lists. And there's no reason I can't listen to music while doing it, it's more fuel for them.