It's like a cutie mark. How do you know till you find it? I've honestly never felt more sympathetic to the cutie mark crusaders, the last one even more so than the two who get theirs first. My two best friends are going into vocal music and neuroscience. I'm the only one left.
I have many majors I'm looking at, but these are my top 3 with explanations.
1. Engineering (general): I love solving problems. Just as simple as that.