Why Is It So Hard to Be Rational?

I met the most rational person I know during my freshman year of college. Greg (not his real name) had a tech-support job in the same computer lab where I worked, and we became friends. I planned to be a creative-writing major; Greg told me that he was deciding between physics and economics. He'd choose physics if he was smart enough, and economics if he wasn't--he thought he'd know within a few months, based on his grades. We roomed together, and often had differences of opinion.