The Mirror. I'm not ancient, but I'm old enough to have lived in the cassette tapes era, so what we were doing at the time before widespread CDs, Napster and all that stuff was copying each other cassettes, and rounding up the running time with whatever song(s) just to not waste the tape.
My cousin was more advanced in his musical tastes at the time, so he sneaked DT songs at the end of the cassettes he was making for me, I remember he put Hollow Years and Anna Lee (at the time, the newest easy ballads) and on another cassette he placed The Mirror; I spent 4 months or so listening to it, and finally it clicked... I liked the song... I loved the song... and well, long story short, it was the avalanche effect that led me to love Dream Theater's music.
All of this was happening during the spring / summer of 1999, I didn't even had internet at the time, but I became a very devoted fan and somehow I got notion that on a certain day (ironically, exactly 16 years ago) the new Dream Theater album was going to be released, and I already decided for a blind purchase on release day.
So, again: it was 1999, without internet all I knew was the release day of the new DT album, and I walked into the store knowing exactly that.
I'll let you figure out the rest