You forgot about a house-related detail, like toilet paper, cups, or space for guests to store their coats.
To avoid this problem completely, make a list of small tasks to check on the morning of the party: Stock your bathroom with extra toilet paper. Locate spare napkins and cups. Clean out your coat closet or find another space for guests to leave jackets and bags. We tend to focus on the food and drink when planning a party, but making your space feel welcoming is just as important. If you forget toilet paper, pick an understanding friend to watch the food while you run out and get some—or send her to the store. If you forgot to clean out the closet for coats, offer to take your guests' things and put them in another room, like your bedroom. If you run out of cups, resort to mugs and jars. Fill the need for napkins with paper towels or whatever small cloths you have on hand.