Any writing course can tell you that one of the most important components of a protagonist are their wants, needs, and drives. I say the same is true for a player character. Unfortunately, due to the compromises inherent in creating a personality only tangentially related to a plot narrative that the player knows little to nothing about, this is the one area most often glossed over or abandoned in favor of providing the Game Master greater ease in propelling your character forward through the story.
The trouble with that is it often leads to rather aimless characters who aren't particularly motivated to stay on the railroad tracks but require the tracks to keep them off the couch watching Daylight Soaps. This issue can particularly plague characters made along 'realistic' lines as most people would realistically avoid danger for safety. Of course, one can argue that the game world is full of such realistic characters. They're called NPCs.
A PC is a protagonist. An internal motivation and propensity to act makes for a far more compelling character than one who has to be dragged along through sucker punches like 'kidnapped loved ones'. And such motivations can be quite vague. Think of the differences between a Ventrue who has a higher order drive toward Perfection, Control, Power, Possession, or Affirmation. Sure, their personality might be somewhat the same, but there'll be lots of little distinctions between HOW they behave and what choices they would make.
Of course, I think part of the blame for de-motivated PCs rests with the Game Master. It's difficult for a player to fully understand what sort of character would work in the game (presuming it's a character type they would even enjoy) and it's doubly hard for a group of players to create characters that are actually complementary with each other. So the compromise is to create characters that make fewer waves by wanting 'what the plot wants them to want'.
So, to put my money where my mouth is, my next post will involve me creating a multi-faceted and motivated character to insert into a Pathfinder pre-written campaign. I'll then let you all know if it works out to be complementary rather than problematic, given that we're obviously 'on rails' to a certain extent. If I can pull it off there, the rest of you can pull it off anywhere (presuming your Game Masters aren't complete turds).