What did you not put in your thesis?

As my submission got closer there were several ideas I worked on which didn’t make it into my thesis. One little project was just too big in the end, and I couldn’t find a way to explain it concisely. One I chose not to pursue because it was just a restatement of ideas in a different way. And one section was a nice idea that just wouldn’t add much to the overall value of my thesis.

Reflecting with years of hindsight: the reasons why I didn’t include something stand in stark contrast with the things that I did include in my thesis. My thesis made contributions to my field. I judged, with support from my supervisor, that the things I left out did not make a meaningful contribution compared to the things I kept in.

If you’re finishing your PhD, what are you leaving unwritten? Why is it staying out? How does it compare with the work that makes up your thesis?