Hindsight Bias

Ok, looking at this problem you have no idea how to solve it. After listening to your teacher telling you how to do it, you'd say "I knew the answer was that all along". If you knew it then why couldn't you do it on your own? The answer is that you couldn't see the answer coming so you'd make up a reason to mask your "stupidity". This also applies to 9/11 when the people thought they could have seen it coming.

Hindsight Bias: tendency to believe, after learning of an outcome, that one could have foreseen it.