I can't know

I got my Trig test back yesterday. I cheated, (not on the test) I picked it up yesterday in Brother Saunders office instead of waiting until he passed it out today in class. I got a 90/100, which overall is not bad. It is actually one of the higher grades in the class. But what drives me mad is I completely forgot to answer the first question, worth four points. I would have had the highest grade in the class if I had only answered the first question. I didn't even see it and I knew it. The first question was the easiest. Idiot! Brother Saunders flat out asked me why I didn't answer it when He knew I knew the answers. All I could think of, "I can't know." this is a phrase I used to use when I was younger. My mom always wondered, "what does that mean?" Anywho, it is cosmic irony. I've decided. I just learned about this in my intro to Lit. class. Cosmic irony is a discrepancy between what the character aspires to be and what universal forces provide. That is it, the universe is against me. I can't know why I make the dumbest mistakes on my math tests, but I always do. Way to be consistent.