I like chemistry a lot...especially O Chem. But some of my other prepharm friends like Biology more. I'm not sure there are set subjects that lead a person to believe that they will automatically like pharmacy. I've worked in a hospital pharmacy before and I really enjoyed it. Plus I'm interested when a pharmacist tells me about a drug: what it does, how it works, what it's for, etc.
At first (years ago) I thought I wanted to be an Optometrist. I was in Walmart and walked by the eye place there so I picked up a pamphlet on eye diseases...since, obviously, that would be of interest to me. I couldn't even read the whole thing because I was just not that interested. But I enjoy reading about drugs.
You just have to test the waters in different ways and in different fields before you KNOW it's for you.