Students' personality traits are among the most important determinants of students' choice of major and their satisfaction with that major. A survey of 849 students at three public universities and one private university in two regions of the United States finds that a student's personality also affects the power of non-personality influences on the choice of major. These influences, in turn, affect the likelihood that a student will be satisfied with the major. These findings will allow academic advisors and counselors to draw additional value from personality measurements often used in helping students choose their majors.