I have a few noteworthy examples.
- I only got in to the Harvest Moon series because my import guy back in Derby never got in the later Sonic Advance titles, so he offered me a deal. Check out this new game he had in, Harvest Moon Friends of Mineral Town, and if it sucked balls beyond all repair, he'd exchange it for Sonic Advance 3 when he finally got it in. I never took that game back, and now I follow the series like a stalking assassin.
- I got in to the Ace Combat series while hunting for Dancing Stage Fusion for the PS2 for my girlfriend at the time, the guy behind the counter pointed out Ace Combat Squadron Leader (from which I get my name) fresh in behind the counter and the rest was history.
- I was drawn in to the Final Fantasy series when a friend of my brother offered to loan my Final Fantasy 7 in exchange for me lending him my Pokemon Red. I still have that exact same copy of FF7 to this day. God knows what happened to Pokemon Red.
- I originally only started playing the Mass Effect series because my old man was being an arse hole about it. He'd been looking forward to playing it for months, one of the few games he ever got excited about, but he was also being a complete tool in every possible way, so I blasted through it over a weekend just to piss him off about finishing it way before he did and knowing how everything he was doing was going to play out.