In which I laugh maniacally:
It doesn’t really matter how much you want to accomplish today; your pace will likely be set by circumstances that are beyond your control. The best you can do is remain clear about your abilities and your limitations. If you don’t overcommit, all should work out okay. But if you take on too much, even the simplest jobs could suffer. Pace yourself, work hard, and don’t apologize for what you cannot do.