In the preliminary matches, everyone who lost was out for good, right? But how does it work in the stadium? If everyone fights everyone else and everyone who loses fails the exam, then only one Genin will become a Chuunin. And if not, then why is everyone so intent on winning when they could afford to lose a match or two? It probably has to do with something like "Ninja Honour", but if two people who liked eachother, like Naruto and... Lets say Hinata even though she's out, would one of them HAVE to fail?