I stared at a printed worksheet for a solid thirty seconds wondering if I did it with the class already.
I hadn't. I did it last week at another school. And I did it last year with the students at this school who are now at another school.
So, things have been done and they will continue to be done. And I am oh so glad that I write down everything that I do so that mistakes are not made.

Of course, there is the moment of terror when a student goes "We already did this." but more often than not they are refering to the fact that we are going to first review what we did last week.

In nine years I have never repeated a lesson to the same students twice in a row by accident. And yet I constantly fear that I will. I'm not sure what exactly would happen if I did. The students get a bit more practice. I get a bit more practice. They would possibly think me a bit silly, but I'm convinced they already do.