The problem is, we're dealing with human beings. Its all good and well saying just do this but who really isn't affected by other teams results, the way a game is going for us etc. We're all human, if you're watching a game and getting anxious it will show, unfortunately as much as the whole 'one game at a time' is a great idea, in reality you won't see any fanbases actions reflect this kind of attitude ever.
I'd love it to just be remaining calm and just willing the boys on all game every game but no one does that, especially with whats at stake. Its admirable to want that and we all do, but its just not really realistic... unless you're a robot. Its the right kind of attitude and way to think about the game, that side of it is realistic but during actual matches, logic goes out of the window at times