I was thinking in the reason why some days we achieve so much and some days we feel at the end of the day that we didn't do anything.
I believe that one of the main reasons is that we don't make any progress or feel like it.
if I could give advice to myself and you, it will be:
Plan the day ahead. I know that a lot can happen in a day that can change your plans. But an small strategy can give you a direction and can help you in not wasting time.
Another suggestion it will be to keep a record of your activities, it does not matter if they are vague, the only important thing is that you know what you did at the end of the day.