Because mere mortals cannot be wise at all times, even the wisest among men make mistakes.
The motto of Worshipful Company of Salters is 'Sal Sapit Omnia'.
The motto of Rainey Endowed School is 'Sal Sapit Omnia'.
A male donkey is called a jack.
Lucas had a little bit of the back story in his head when he wrote the first trilogy, but he originally wrote the original stories. So, he made those and then expounded on the back story later.