This is not because I have never turned in a piece of work that was worth 100%. I have oh-so-many examples, going back to primary school, of tests and exams on which I have met every single criterion, and yet been docked marks for tiny random things that nobody else was. (The award-winner in that respect has got to be my old chemistry teacher's 'this line of your diagram projects slightly beyond this one, so you only got 98%'.)
I have no idea how it would feel to get 100% for a piece of perfect work. But I have a lot of experience in how it feels not to get 100% for work that deserves it.
Demotivating.
It feels like marks are arbitrary, and teachers are only there to keep you down. It feels like ability is its own punishment. I spend increasing hours busting a gut to try and make everything absolutely waterproof only to discover that the goals have moved again, and every time I'm a little more inclined not to bother next time. To coast. To do half-arsed work. It teaches me, not to strive, but that there's no point in striving because nobody wants you to succeed.
But I'm too damn competitive to stop trying, which means I just keep banging head-on into that wall, and I keep getting staggered by the knockback; and honestly, there's only so much of that a person can take.
So... what is it that is so terrible about awarding 100% that it can possibly be worse than the consequences of not awarding it?
(This rant brought to you by the 95% on my latest assessment)
* Actually, this is not entirely true. I've got 100% on quite a few computer-marked tests. Just none marked by human beings.