Last week I took Exam #3 in my Discrete Optimization course. I had no idea how to do the bonus problem but was fairly confident that I'd aced the rest of the test.
I scored 46/50, which is a point less than I did on the previous test. My scores are going down each time, but past performance is no guarantee of future returns!
Once, when as a junior I took Mathematical Modeling, I had an A going into the final exam. I walked out of that final thinking that that was the first final I'd ever aced! When grades came out I had an A- in the course! Hmm, must be a mistake, I'll go talk to the instructor after the semester break. As I was walking down the hall a few weeks later I saw my instructor and started to approach him to and see if, perhaps, obviously, there had been a recording mistake with my grade. He saw me and, with typical military bluntness, said, "Miller! What the f*** happened to you on that final?!"
Confidence is a curse for me.