I'd say discipline is just one factor. Another one is that many of us do poor thinking. When a task isn't well defined we tend to not do it. "Buy milk" is clear

I'd say discipline is just one factor. Another one is that many of us do poor thinking. When a task isn't well defined we tend to not do it. "Buy milk" is clear, "implement backup script with rsync" is not. It may sound somewhat concrete but you have to ask yourself a bunch of question in order to have some clarity as to what that actually means. Often we then feel overwhelmed and procrastinate I'd say.