that if you have, say, two standing meetings, neither of these will be held on the days that you teach, nor will they be held on the same day so that you can go to campus and get them both over with at once.
that if you have office hours from 12-1:30, and your office has thus far been so quiet that you can hear crickets chirp, on the one day when you step out for five minutes to get a sandwich for lunch, a student will come by, find you gone, and write you an email about it.
that if after a diligent search for a book in your library catalog, you give up and decide to order it, you will receive a note (sometimes an indignant note) from Acquisitions pointing out that it's in the library even if it isn't in the catalogue.
that the one student who has been missing in action from class is the only one for whom you, and apparently the university, have no email address whatsoever.
that if the day dawns gray and rainy, and you put on a sweater because it's 45 degrees outside, the weather will turn warm and sunny so that you look like a refugee from December, stuck in the wrong time. This one I don't mind, if it means good weather.