In my work diaries I often put down the word "nothing" for a day nothing was accomplished. I never offer an excuse for that day. There may be a reason why I didn't get anything accomplished on that particular day. Maybe I was driving 5 hours between my two residences; maybe I was teaching and meeting with students. Maybe I was reading something for my project and didn't have anything to show for it in tangible terms. It makes no difference why I didn't accomplish anything on a particular day. What is important is that I know how many days I accomplished something and how many days I didn't.
Learning not to make excuses for yourself is fundamental. Suppose I had really good reasons for not working. I could be sick, or stressed, or whatever. At the end of the week, then, I have either have a list of accomplishments or a list of excuses.