I don't know about how much it takes, I don't think Kaiji really delves too deeply into that. Really, they just go about showing that in the end, pretty much everybody will choose themselves over some schmuck they just met. (Kaiji, AKA Jesus Christ, aside.)>without any direct reason?
Don't know what you mean there. Every asshole move that somebody has made in this show has been for reason. Sure, us casual observers and those on Kaiji's side think they got the shaft, but again the show's real point is to show us that if we were in that postion, we'd do the exact same thing.