I was just going to mention music. I learned some piano as an adult. I was never able to accept that the same note positions on the treble staff had a different value on the bass staff. Yes, I understand why it's so, it's just terribly user-unfriendly.

Also, in keys other than C, I felt that it wouldn't kill them to mark every instance of the sharp and flat notes, instead of doing it once at the beginning and implying it everywhere else.