I skipped a class (went from 3rd standard to 5th) because I could clear the entrance exam during changing schools (I also topped the exam, mainly because my tutor made me work hard). In college I failed a paper because I was lazy and didn't work hard. The first incident made me happy but didn't make me think that I was very smart and the latter didn't make me think I was dumb. I knew the reasons exactly. We under-estimate how much we know ourselves.