Another problem with passion is bias.  Especially in social science, people pick topics in order to convince the world of their one true answer.  But it is healthier to focus on questions, not answers.  By picking an answer before you’ve really studied a topic, not only are you more likely to be wrong, but more important, you could miss interesting new angles.

My colleague Bryan Caplan is the sharpest thinker I’ve personally known.   He has a penetrating insight and willingness to embrace uncomfortable conclusions, except on a few topics, such as free will, dualism, and libertarian ethics, where he developed strong intuitions early.  Fortunately for Bryan, while these opinions may motivate his research, he had not directly worked in those areas.  Similarly, I have to admit it was good that I spent most of research time away from the topics I was the most passionate about.