So what if he was a little paranoid? After working at the CIA for a few years, it becomes part of the job description. In his time, he was a good operative, one of the best actually, and some things change, but the paranoia never really goes away. The fact that Auggie Anderson couldn't see to save his life, literally, only made the situation worse.
So what if she was a little overachieving? Being the little sister of the "golden girl" had its perks, but mostly, she was overlooked, by everyone. To compensate, she made it her life motto: Do better than Danielle. Sometimes it was hard (Dani always did have the better luck), but most of the time, especially at the CIA, she could be better than her sister, and still enjoy life, at least a little bit. Don't mistake her feelings, Annie Walker loved her sister dearly, but sometimes it felt good to be needed and noticed.
Who knew that the paranoid ex-operative and the overachieving newbie would have anything in common at all, let alone balance each other out so perfectly?
Auggie certainly didn't, not when he first gave in to curiosity and talked to the supposedly beautiful woman Conrad was attempting, unsuccessfully, to snare.
Annie certainly didn't either, not when she was learning self-defense from a blind, yet still incredibly good looking, tech operative.
The CIA encouraged in-house dating. Coincidentally, they also encouraged paranoia (it's never a good thing to get oneself killed), as well as overachievement (because you've got to start somewhere to get to the top).
Of course they didn't start out that way; they were friends way before either one of them really became interested. Although, emphasis on the really, because there's something awfully appealing about an overachiever in kitten heels, and Annie can't deny the initial attraction she felt to Auggie when he checked her out that first day, chalking it up to "being paranoid" and "careful".
Their relationship is kind of unexplainable, really. They aren't supposed to be compatible; they weren't even supposed to get along. But that's just how they work: he's paranoid, but she sees for him, and she's an overachiever, but he's taught her how to relax and enjoy life.
Some people don't understand what Auggie has that makes her love him, or why Annie would choose him over Conrad, or Jai, or even Ben. Danielle didn't even see it coming, and Ethan, the strange guy from the Smithsonian, didn't even have a chance.