I just noticed the other day that the more there are new players on the other team, the less I can be useful for my team. Why? Because, as Spy, it's a matter of anticipation (at least, for me), but new players act in such unpredictable way sometimes... They flee from the weirdest situations, they get lost on maps, they generaly have poor aiming... All factors that drive them to places I can't anticipate, that make them turn around when I'm about to backstab them or that makes me die from random shots that never aimed at my invisible self.
Does the same happen with people who use different classes? I mean, do you die because of unpredictable moves from new players? o.o