How do you determine when to load your daily schedule with more tasks, especially those very demanding ones?

I started loading tasks I have already tried in the past such as exercise. And then decide on a number and type of minimum exercises for the morning

I prefer to challenge myself. I give myself more assignments than I can fulfill in the first place but will be able to fill after a short time. I set my goals up front. What's important to me is not to be bothered if I don't check everything on the day. I know that soon will be the time I tick all the boxes.