… You hear a great piece of music in a clip for a film, buy the soundtrack only to find that the music is not on it, spend weeks trying to find the music through various means, give up, wait a couple of years, buy a CD completely at random, find the track you were looking for a few years ago is on the CD you bought.
It happened to me. When the Matrix came out, the clip of the scene where they are in the lobby of the govornment building had some very cool music playing with it. I bought the sound track, not on it, spent weeks trying to find it with no luck, now, a couple of years later, I bought “the cross of changes” (enigma) and found the music I was looking for! (track 2 if I remember rightly)