Blunk

Mr Blunk is the famously surly coal porter at Unseen University. He works under a fundamental misconception based on starting with first principles but making an incorrect logical deduction.

If the name on the door just reads "the Dean" or "The Senior Wrangler", then Mr Blunk correctly assumes only one person is in residence and leaves only one bucket of coal.

If, however, the sign on the door reads

Egregious Professor of Cruel and Unusual Geography
Professor of Slood Dynamics
Fretwork Teacher
Chair for the Public Misunderstanding of Magic
Health and Safety Officer
Professor of Virtual Anthropology
Lecturer in Approximate Accuracy

Then he counts up the number of names on the door and leaves seven buckets¹. No amount of logic, reasoning or request is capable of shaking Mr Blunk out of this.

Now Rincewind has nineteen academic titles, wished on him by the rest of the Faculty in a spirit of schadenfreude, it could get quite warm down his corridor after the sign-writer has been to add the rest.

¹ I.e. a Coal Porter medley...