Well, ultimately, it is both. This is both an answer for all people, and myself.
I was brought up in podunk-ville, USA, without cable television or a plethora of radio stations. By accident of birth, I was subjected to Country music. Go ahead and laugh, but it was not like I knew any better, it was just something that my parents listened to and I did not know any better. Now, the country I was brought up on was not this pop-inspired stuff that continues to flourish in the wake of Garth Brook and Billy Ray Cyrus - it was this old-timey stuff like Hank Williams, Weylon Jennings, and David Allen Coe. Honestly, some of it I still enjoy and have an appreciation for, if only for nostalgia's sake, but for the most part... Well, let's just say that Country and I are never ever getting back together.
When I was in either 4th or 5th grade, one of my older sisters introduced me to Metallica's ... And Justice for All album. That was something that put its hooks in me. I really enjoyed the aggressive tone and heavily distorted sound of the guitars, and, beyond that, it was a fairly technical album. There was a lot to appreciate and keep you interested - which is volumes more than what I can say for the pop music of the time, or currently. (What the hell was even considered pop back then? I don't even remember.)
From Metallica, I remember branching out to Pantera. I think I was over at a friend's house and I had heard Domination, so decided to pick up an album, which ended up being Far Beyond Driven. At first, I honestly did not like it. The sound and tone was a lot more raw and I was not sure what to think about it. I mean, look at it this way: I went from a group that used topics like the works of H.P. Lovecraft, mutually assured destruction, and books like Johnny Got His Gun, to a group with song titles like "Use My Third Arm." Part of me wants to say that, even at the time, I found some of it immature, but I also know that there were aspects I did not understand. Either way, it grew on me, and I ended up buying all their albums - even the ones that were pre-Cowboys from Hell. (Ha!)
After that, my tastes blitzkrieged out. I simultaneously got into Nightwish, who had just released their second studio album, and a bunch of bands like Dimmu Borgir and Siebenburgen. I think the first Amon Amarth Album came out at around this time. There were also some other bands like Suidakra and Vintersorg that I really liked. Basically, I ended up picking up appreciation for different types of metal: operatic, folk, black, dark, death, doohicky. Whatever labels you want to put on it. I was mildy interested into categorizing what genres were what, but I did want to find out all the different aspects or styles people experimented with to produce good music. With that mindset in mind, I remember also doing a kind of historical survey, and picking up a bunch of albums from Black Sabbath, Iron Maiden, and Judas Priest.
Sometime shortly after that, I remember my older sister (re)introducing me to Tool. I remember her listening to it before, but it was just a couple songs from one of their albums. When I started actually listening to them, it was shortly after they released their Lateralus album.
With some Music Appreciation classes taken at university, I delved a bit into Gregorian Chant/Organum, and some of the varieties of Classical Music. Seven years later, that is pretty much where I am at today, although I have picked some some more bands and playlists along the way. I've given a lot of different stuff a pretty decent listen-through, most noteably things electronica-esque, but rock has always been my core since my introduction with Metallica.
EDIT - some spelling corrections, and somehow I forgot to mention god-damn Motorhead, so I'm putting that here, lest I hang my head in shame forever.