I'm back to teaching a course that I know well. I became the course coordinator and oversaw the transition to large sections, then taught all the sections exclusively for a year. I spent another year splitting the course with someone else and teaching them how everything I built worked. And I've come to realize that sometimes I make more mistakes with things that I know really well.
There are all these little niggling things that I figured out in the first semester: bugs in software, common student errors, problems with the schedule, etc. By the second semester, I knew where all the pitfalls lay. I had fixed the bugs that could be fixed and warned students in advance of the problems they were going to encounter.
And by the third semester I forgot them all again.
I have had a lot of "D'oh!" moments after the first two semesters. Those times when I start getting students e-mails and suddenly go "Oh right! I needed to tell them to install Java on their computers..." Or: "Whoops! Forgot to teach them about order of operations again."
I guess I figure I've been doing all this for several semesters, so surely they must know it all too. (To be fair, there probably are some students who have been taking the class for as many semesters as I've been teaching it, but I try not to dwell on that.)
But today I remembered something I usually forget, so I'm ahead of the game for the moment.