For me, it was this very cassette of The Rite of Spring.
I wasn't into CM at all, but back around 1986 or so, when I was about 15 years old, I went to the record store and found this huge bin of $1 cassettes. I bought $20 worth, at random, just to fill up this huge empty wall cassette rack that I had.
Over the next few weeks, I'd occasionally put one on while doing homework. I paid no attention to the music whatsoever...it was just background stuff.
But then one day I put this on, and everything changed. I had never heard anything like it.
I've held onto this very cassette for the last 35 years, through numerous moves, marriages, careers and kids. It sits with pride on my shelf. I can't remember the last time I actually listened to it, but I know I'll always hang onto it.
Do you still have your first album? Or remember what it was?