You know, as a LL, Pony, and now HS ump since I was 16, I can tell you it's easier than you think.
The other day I called batter's interference on a throw to 2B after a goddamn ball four. It wasn't until the coach walked up calm and said, "Blue, that was ball four." I stopped for a second and was like, "Oh, well, scratch that. My bad."
It happens. I have sympathy for umps.