Reeve was, by nature, a perfectionist. He wanted his every endeavor to be done to its best potential, and so, usually ended up worrying that whatever he ended up with was not good enough. It happened all the time with his computer science classes, and students and teachers alike constantly reassured him that the classes were going well.
And so, when Reeve got the request from the principal to be a substitute for a math class that day, the man was fretting over whether or not he still remembered the finer details of calculus to teach a class to par.
He made it into the room before the students and read the note from the teacher (they were going over trigonometry, thank God) and nervously fiddled with his papers, getting everything organized. He was not obsessive over things like this. No. He had finally just settled down in the chair behind the desk when the students finally started filing in.