Supermom strikes again

Some things I did today:

1. Went to work: cleaned up laboratory, prepared class materials for next Thursday, taught 1 seminar and 1 lecture
2. Fetched my daughter from daycare
3. Delivered tax return to revenue bureau & got a little stamp that proves I did it
4. Bought groceries
5. Laundered diapers
6. Loaded, ran, & emptied dishwasher
7. Played with and prepared snack for my daughter
8. Walked the dog
9. All the usual (nursing, snacks, medicines, bedtime, etc.)

Why is it that some days I can do so much and other days I seem to accomplish nothing tangible?