User blog comment:Jojo-a-gogo/What do you think your nen type would be if you had nen?/@comment-1029419-20121023051111/@comment-174.95.73.46-20121024083415

Because even though every human being contains a trait from all 6 categories, one trait is more seen or commonly used that the others, that trait is the dominant trait and the one which determines your category.