To put a finer point on it: you are not a “good boy” or “good girl” for completing all the items on your short list any more than you are an unproductive person for not ticking off every item by the end of the day. It may well be that you focused on exactly the right things each moment of the day without striking through a single item on the sub-list. Simply having those short list options to hand can help you to validate that those choices you make which are not on the list are, indeed, correct – because you have consciously weighed them against that shortlist before acting.
This is a great mindset to have about the Today list functionality in Things. I like that Robert calls it a daily sublist which sounds way better than the "I have to do these today no matter what happens" list as people like to think about it usually.
I'm also in the habit of curating a weekend chores list from my main Home list into Things' Today view. I do this because my biggest problem with GTD at the moment is sometimes I forget to review my appropriate context lists on a daily basis or at the right moment.