"You got a 100% score, i'm going to give you a 99% score because nothing's perfect"
"I believe that nothing is perfect and i am completely fine with giving you an inaccurate grade if it means i get to shove that belief down your throat."
"Nothing's perfect, even though your test score is perfect."
Someone did something bad, and the teacher doesn't know who it is.
The teacher gives the entire class detention instead of recess/break, hoping that whoever did it will confess, despite the fact that there is no personal gain to confessing and the confessor will recieve a worse punishment if they confess.
Usually, either nobody says anything and all but one of the class members receives punishment for something they didn't do, or a person who didn't do it gives a false confession so everyone else can go.
This happened several times when i used to go to school, and in none of them did the person who actually did it admit so.