Before I realised I was aromantic I thought I was asexual. I actually dismissed aromantic at the time because I tried to imagen what it would be like to not experience romantic attraction but I just couldn't. Turns out that's because I was trying to remove an experience from my life I had never had, hence finding it impossible to do.
And why did I think I was asexual? I have no idea, it's a complete mystery to me. (Although if anyone has any ideas I would love to hear them)