It partly has to do with the fact that you are so used to "breezing" over classes and progressing that you fail to realize that there could be people smarter than you. There is always a limit. And you finally have to start working hard. Trust me, your IQ is probably the top 1% in the world (http://www.iqcomparisonsite.com/SATIQ.aspx) so it will take you some time but you will reach there. And the ones who answer in the class aren't the smartest. It is my experience that half of the people who nod aren't even paying attention! :)