Writers carry notebooks because good details disappear in an hour. So do good feelings.

Specifics have a short shelf life. The exact thing somebody said, the light on the way home, the particular relief of finishing something: within an hour it has all collapsed into a general sense that the day was fine. Feelings go the same way, which is why a good week can leave you with nothing to point at.

Keep one line a day somewhere, and keep it concrete. Not that practice was good, but that the coach said your second half was the best he had seen you play. Three weeks of that gives you something to read on a flat day, built out of evidence rather than mood.