If you believe in the efficient markets hypothesis, then you should not be considering a career in sales and trading. An old joke about the hypothesis goes something like this:
A finance professor and a student are walking down a busy sidewalk. Along the way, the professor is discussing efficient markets with his student, who is staring down in studious thought. The student catches a glimpse of a $20 bill on the sidewalk, and he stops to pick it up. After pocketing the bill, the student runs to catch up with the professor. The excited student asks the professor if he had seen the bill, and the professor, without skipping a beat, quips "My dear student, have you not been listening to any part of the efficient markets that I've been talking about? Yes, I saw the $20, but I knew that my eyes must have been deceiving me. Efficient markets theory dictates that it couldn't possibly have been there, since someone else would have already picked it up."
Of course if you've read this far, then you probably don't believe in the efficient markets hypothesis, and you may even be willing to wager your career on it.