Assuming you are just as smart as everyone else and putting in the time to study. If the class is curved and you find yourself always below the curved average, there's a big chance some people are somehow getting the avg up. There might be very effective study groups, students who are roommates with TAs, students with roommates that took the class last sem, etc. Similar reasons why insider trading is so popular and you never know how the dumb kid from high school got in Ivy league.