Dr who spoiler
Does The Doctor have some kind of Time Lord ADHD that means he can't focus on a simple "guard the master for 1000 years" task without getting distracted by all the interesting humans, and therefore needs Nardole to keep reminding him of what he decided to do.
Maybe the doctor is just a totally inconsistent character, written to have all/vague characteristics to appeal to the widest audience. Can you think of a single personality trait the doctor has consistently?