A guy named @TheAlsoran posted the following text on Twitter to Amy Hennig, Creative Director on Uncharted 3, to see that if his/her interpretations were correct.
Chloe and Sully are in to adventuring for the money, all three games make that pretty clear. In this latest entry they see the odds piling up against them and try to persuade Nathan to let this one go as there's easier ways to make money. But he doesn't stop, even when his friends are threatened and hurt, because he's not interested in monetary value; even in the flashback, young Drake doesn't steal the ring to sell it.
(As an aside, Cutter is more in-tune with Drake's ideals than the other two.)
Then we meet Elena. Clearly she and Drake got very serious and then broke away from one another entirely, and if you listen to her dialogue — especially before they head down the well — it seems it was Nate's need for adventure that came between them. He put that need before love.
So, he's not driven by money and he's ostensibly willing to sacrifice everything he cares about to see things through. Why? Marlowe has the answer.
Nathan Drake isn't his real name. He's not a descendent of a long dead adventurer, but an orphan from a troubled background. An orphan that became infatuated with said great adventurer, after which his institution was named. He was someone drawn to an idea: "Greatness from small beginnings."
Nate's entire existence is built upon a lie, a deception that lead him to meet Sully and Elena, the two most important people in his life. He is defined by an imagined relationship to Sir Francis Drake, a name which he would do anything to live up to. Which is why he has to see how deep that rabbit hole goes, has to prove that he's a worthy enough adventurer for his assumed surname: everything he's done and everything he has are tied up in that lie; without it, what is he?
Psychology is in the everyday, it permeates everything and everyone. Anything with well written characters will take it into consideration, even light-hearted pulp.
In response, Amy Hennig said:
The stuff in the spoiler text is pretty much spot on.
I just thought it would be nice to share that even though people might think that the story is shallow or pulpy, there is a lot of thought put into characters and their motivation for their behaviour by the writer(s).