Flexibility

When you begin with a rigid schedule and are afraid to deviate from it, you may be placing a burden on yourself you do not need. Now you need some set goals and plans and timetables and schedules. But building in flexibility allows for some flexibility required to handle emergencies and unplanned, spontaneous events.

I am arguing for a happy balance. Franklin Covey does an excellent job illustrating this: put in the big rocks first and let the little rocks fall around them. Let's say the little rocks are the flexible things. The big rocks are the absolute must-do tasks. 

So when planning a week, a month, or a year: allow for the little rocks.