Good teaching involves stealing and lying

I was visiting my undergraduate institution and chatting with a couple of my former physics professors. Bob and I were talking about a new course he was developing. I recalled a conversation with my favorite high school English teacher, who told me that "good teachers steal all the time" -- meaning that you should not be afraid to take good material from other teachers. Bob remarked, "You also have to lie all the time. Small lies because you don't want to get bogged down in details." Here's my interpretation of Bob's statement. Physics, like any other science, is an evolving subject filled with exceptions to the rule. You don't want to present all the complications to a first-time learner. Not only will your students get confused, you will probably get confused, too! So you end up glossing over details and giving your students a clean, admittedly sanitized version of the story.