Even worse, You create a complex NPC with a full plan, but the PC are in a murder hobbo mood and just kill them, Then you have Bolin the Goblin, who suddently beg the PC for mercy, and someone wants to spare them, so now you have a whole session role-playing with *Bolin the Goblin*

I've learned that NPCs should have the bare minimum of background necessary for my sessions. If the players like the NPC, it they become useful later on, that's when I start fleshing them out. Of course, the NPC needs to survive long enough for that to happen.