Calendars are quite different from plans.
First of all, calendars are mere tools, whereas plans are made of content. You fill a calendar everyday, but with no plan what do you fill it with?
Second, calendars help you trace your activity by the day, whereas plans can have a much broader view of things. Your daily tasks are worth nothing if you don't picture the horizon that gives meaning to their own fulfilling.
As far as I'm concerned, and as important as it is for my personal organization, a calendar makes me feel constrained in the work I do. On the other hand, a plan makes me feel I can start something from scratch and develop a clear view of things to come. Calendars are a big deal, but they are far too detail-oriented for a mid to long-term view (and you're reading the words of a detail freak).
Two thoughts about this:
- Don't focus on filling a calendar. Focus on following a plan.
- I don't know what is harder: defining a plan or realizing you have to let go of one.