The title says it all: how were you first introduced to KSP? And got you hooked so much that here you are, in the forum, reading this post?
In my case, I am a big fan of management and simulation games. At one point I was playing Minecraft and I was on the internet searching for games similar to Minecraft. Came across a website that described KSP as 'The Minecraft for Rockets and Space' and the rest is history.
I've been playing KSP intermittently since 2014. My steam account says I've accrued 113 hours (actual number should be higher, considering sometimes I'm offline and excluding the hours I've spent playing the earlier non-Steam versions). Every now and then my work would take me away from KSP up to months, but this is the one and only game that I keep finding myself coming back to.