Better to lower expectations and then over-deliver than to fail to live up to them.
In the bookshop I work in we tell people that the delivery of an order will take one to two weeks. Sometimes books arrive within a few days, and customers are delighted. But there are the odd occasions where they take the full two weeks. But if they do, the customers are still happy because it was what they expected. If someone wants something for a gift, we cannot guarantee it by a particular day because deliveries by suppliers are out of our hands. Better to be realistic than to let people down.
The same applies with our expectations of ourselves. Maybe we need to be more realistic or more caring of ourselves. Stop trying to do too much and running ourselves ragged. Most things on your to-do list can wait a day. And if they can't, do those things first!