This has really caused me to think. End result: I have no idea what specific event, if any, caused me to get into knives. As far as I can remember, I've always had a fascination with knives.
Growing up, my parents never carried a knife on a regular basis that I knew of, not even a little SAK...though my father always had/used utility knives and box cutters for many various tasks while working (but those never really piqued my interest). I do remember my brother having a few knives including a yellow SAK, cheap balisong, and an unknown type of lock-back. These definitely interested me, but the interest had already been there. When I was about 13, I found what I remember to be a small Spyderco folder which was subsequently lost. I don't know if it was the real deal since it was so long ago, but the blade was maybe a 2 inch chisel grind and had blue plastic handles with a Delica-type pattern.
During my late teens, I had multiple different knives ranging from a couple of Gerber Paraframe IIs, a CRKT M16 variant, a couple of fixed-edge Bucks, and a fixed-edge Kershaw Echo (I believe). When I got older and had the magical thing called a job where they give you "money" for doing things (I know, it's hard to believe...this "money" is still somewhat elusive since it disappears so easily from me). When I had this "money," I would go into Academy or Wal-Mart and look at the knives, and as such, brought home the above-mentioned knives.
I became more fascinated with the higher-end knives just a few years ago. Even though I had bought a Leatherman Surge nearly a year prior, my first "expensive" knife was a Kershaw Shallot in Sandvik 14C28 for about $55. I spent about six happy months with just my Vic MiniChamp, Shallot, and Leatherman until I got interested in the Vic RescueTool (was a vollie firefighter). Because of research into the RescueTool, I found out about Benchmade and other high-quality knives and have been lighter in the wallet since.
Long story short, I don't know of an original cause of my interest, but it has always been a presence...and I definitely have a lot of catching up to do!