If you want to be the sort of person who'll do X given Y, then when Y turns up, you'd better bloody well do X.

I think this describes one of the core principles of virtue theory under any ethical system.

I wonder how much it depends upon accidents of human psychology, like our tendency to form habits, and how much of it is definitional (if you don't X when Y, then you're simply not the sort of person who Xes when Y)