This is an illuminating topic. The things that all lead us here are varied, and often very fun.
A little while ago, I made a poll for this purpose, so I’ll share it here. I don’t plan to ever close it, and it can change over time. =)
Personally, I started with JP gym decks. A friend in a performance gave all us kids PkMn cards, and then I bought the game; fought with another kid over getting ripped-off in a trade; marveled at seeing PkMn Red in Japanese; etc. Always kept my cards, but didn’t do much new collecting after middle school. More recently, senior year of college I got back into collecting and picked up a booster box of skyridge. made my money back and decided I was going to be the very best. Then I discovered Scott’s illustrator and trophy pikas, and my eyes were opened. 