it is very important to prepare and plan for each lesson in conjuction with that you (the instructor) must keep also in mind that your preparation and planning is well researched for each student, every student is different and understand at his/her own pace. as an insturctor you should/must shift gears on a regular basis to reach each and every student in your class. its great that 90 percent of your class understand the topic at hand but what of the 10 percent that did not, you have failed to prepare and plan... 100 percent accountability. is your objective and goal.