
On the other hand, she has plenty of evidence to think Lazarevic is insane. Also, Elena saw exactly how El Dorado's "curse" worked, whereas she had no idea about the details of the Cintimani stone's own curse or even any evidence that the stone itself existed.You'd have to be touched in the head to think everything supernatural is true just because of one instance of seeing something like a zombie plague. Also she had no chance to be skeptical about El Dorado - she didn't even know what it really was until after they'd encountered the mutant Spaniards - whereas she's known about the "curse" for a while and dismisses it as an urban myth.
Arbitrary Skepticism at its finest - while she saw for herself what the El Dorado "statue" did, it could be that she's still dismissing that as a one-off and refuses to believe that on her next big adventure, she will once again encounter something supernatural (after all, in reality what would the chances be?). Elena at the end of the game doesn't believe the "curse" of the cintimani stone, however this is the same lady who saw what the stone does to people, but more importantly the events of the first game!!! She forgot what she lived through or what?. It just makes me wonder if Harry was using Nathan in the past and only Nathan thought they were friends. I could get him being fearful of his boss' wrath, but he seems to take pleasure in bringing Nathan down every time he can. So what's the deal? I could understand if it was an 'did what I had to do' moment, in that he hadn't made any progress and Lazaravich's trigger finger was starting to itch. Nathan clearly trusted Harry enough to do the museum heist with him, so he doesn't seem to have any misgivings about Harry prior to his betrayal which would indicate there had been some bad blood between them in the past. He sells you out, shoots you, and even when Lazarivitch betrays him he chooses to try and kill you and Elena rather than hopefully seeing the nutcase he works for taken down. But once you get to the end of the mission and Harry betrays you he just seems to straight up hate your guts.
Harry even mentions during the museum run that it's just like old times, clearly showing they've done heists like this before.
What is Harry's gripe against Nathan? When he first shows up he's friendly and cheerful, and the two talk like old best friends.