This might not be the best reason, but I was having a terrible day at my home university. I haven't ever really felt comfortable there, and one day last January I felt particularly out of place. I didn't want to finish the semester, let alone return in the fall, but I knew I had to, unless I went abroad.
I immediately set up an appointment with my university's study abroad office. I needed a school where I could take courses on Ancient Greece and Rome in order to finish my major and graduate on time. That narrowed it down considerably (basically either Cork, Ireland or London, England). I had always wanted to go to Ireland, and didn't know if I'd ever get the chance again, so it was an easy choice.