I've been monitoring my students for the better part of the day, and noticed that one of them, who has been struggling, but improving, over the course of the semester just completed the final exam under the time allotted.
After having marked the exam, I noticed that this person aced it with a greater than 90% score! I was so happy for this person. I'm pretty sure the final marks will be something that will bring a smile to this person's face.
So it's things like that which make me realise how rewarding teaching is. It's really a nice feeling to see someone understand a concept after having explained it to them.
Now I can smile for the rest of the evening whilst waiting for my other students to begin and complete their finals.