Now here’s some advice that’s actually useful:
You probably associate fads with fashion and junior high school, but fads are very much a part of modern academic culture. Whole disciplines and sub-disciplines rise and fall in popularity, as do certain ideas and personalities, the influence of which will often cross disciplinary boundaries. The pernicious effects of this faddishness are most often felt by those who study something that is out-of-fashion at the time they enter the job market. The most savvy (if un-idealistic) graduate students will choose their programs of study and dissertation topics with an eye to what is fashionable. Just hope that your choice is still fashionable a decade hence.