Progress should survive being human.

You will get sick, get tired, lose stretches of time to things you did not choose. Any system for progress that assumes otherwise is really a system for feeling like a failure, because human beings are not consistent machines and no amount of resolve makes them one. The plan has to include the fact that you are a person.

Build in slack deliberately rather than pretending you will not need it. Fewer planned days, a lighter target, an accepted margin. You will keep more ground over a year that way than by aiming high and collapsing.