Being able to plan well is one of the key skills that a teacher needs to have.  It involves being able to imagine what is going to happen in the classroom, and to make choices based on this imagined experience.  Planning also involves the ability to zoom out, to see the bigger picture and know how a 2 hour lesson fits into a 100 hour course, but it also involves the ability to zoom in, and work out the mechanics of how a 15 minute activity will work best.