To-Do Lists are large containers.
They keep everything you need to do at some point in time. They can be very long, and you can add to them continuously.
Must-Do Lists are small containers.
They only have the two or three things you must get done today before you go to sleep. Do not allow your Must-Do List to become overloaded. At most three items can go on it. And then those things must be done today. You should have something on your Must-Do List every day, but no more than three items.