In my case, there were three people or things that sent me down this enjoyable but expensive path....
It started with my grandfather, affectionately known in my clan as "Pop". My parents were Mr. and Mrs. Suburbia; it was Pop who took me into the woods, taught me to fish, taught me to shoot, and taught me that a gentleman should never leave the house without a good, sharp knife in his pocket. Without my parents knowing, he gave me my first knife: an old Scout pattern, with a bail to tie an old hiking-boot lace to, so I wouldn't lose it. Never let my parents see it, of course, but I never went into the woods without it. He also leant me several of his own knives from time to time, mostly Schrade Old Timers or the occasional Swiss Army knife; to this day, the feel of saw-cut brown Delrin reminds me how much I miss ol' Pop.
I lost track of that scout knife eventually*; when I got to high school and got a job, I got me a Schrade LB7, a big, ungainy half-pound of steel and brass and rosewood which seemed to me a more "grown up knife". Never took it to school, of course, but by the time I went to college, I was rarely without it. But other than occasionally lusting after a Buck 109 that I could never justify buying, that was the extent of my interest in knives at the time.
The second influence was a guy I worked with in California, another young aerospace engineer fresh outta school, also working on Weapons of Mass Destruction. He was Filipino, raised in Alaska (his dad was military), and quite the outdoorsman, at least to a sheltered suburbanite like me. He was my main shooting buddy in those days, and he rarely went anywhere without the Spyderco Endura he bought the first year they came out. To a guy like me who was used to those old Schrades, it was one butt-ugly knife. But the engineer in me could see the advantages of the one-hand opening hole, the pocket clip, and the serrated blade. I shortly got one just like his, and put the LB7 out to pasture**. In fact, I was so satisfied with it, and the smaller Delica I bought a while later, that I didn't even look at other knives again for many years.
Then came the Internet...
About five years ago, I found an old Buck Bucklite lockback folder in the parking lot at the mall. I didn't know anything about it, so I started searching the internet for similar knives... and suddenly found out what the knife industry had been up to since I bought that Delica! So many designs, such incredible materials... and since I already had an eBay account for buying computer parts, I naturally started looking for knives...
The rest, as they say, is history.
(*A couple years ago, my grandmother gave me a pile of rusty old knives she found in an old toolbox; among them was that old scout knife! I must've left it over at their house one time when I got older, and forgot about it. Anyway, about a year ago I went at it full-bore with Naval Jelly and a brass brush until I could make out the tang stamp: it was a Case! And since Pop had told me that it had once belonged to
his Dad, it's gotta be well over 60 years old. I got out the wet-or-dry sandpaper and cleaned it up as well as I could, and it's still a fine knife, even with the pits and dings and dents. I even EDC it once in a while.)
(** I still have that old LB7, although the backspring is quite worn, so it sticks up at the back when the blade is open. I still have the Endura, too, although the Delica got lost somewhere along the way...)