The implausibility of doing one's best (another English paper)

This paper is not the best I could write. I don’t believe I have ever done my best at anything, nor do I believe that anyone else ever has.
After all, what does it mean to do my best at an action? If I am truly doing my best, there is no change that I could make that could improve the outcome of the action. But in any action, there is always room for improvement. I could have spent an extra hour writing this paper. Or an extra two hours. Or even longer. If I truly wanted to do my best on this paper, I would have dedicated my life to it from the time I learned of the assignment until five minutes before class. This is not a very likely or desirable situation.
This complaint is, in theory, easily resolved, merely requiring a few qualifying words: “to do my best under the circumstances.” But this merely substitutes the implausible with the unknowable. If I were to state this, I would be claiming to be able to solve an incredibly complex optimization problem involving dozens of variables over large ranges. I would have to account for such disparate inputs as amount of sleep, time spent choosing ideas, time spent writing, caloric intake, emotional state, and many others. Even if I had a miraculously omniscient function giving me the quality of my work given each of these inputs, finding the maximum thereof would be incredibly difficult.
Then there is the difficulty of defining the “circumstances.” What set of constraints should I place on my productivity? Should I allocate a set amount of time? Should I take my emotional state as a given? Should I assume that I had to go to that party Friday night? Should I consider myself responsible for mistakes I made years ago that hindered my intellectual development? Not only are the constrained maxima unknowable, so are the constraints themselves.
If I were to believe that I had done my best on this paper, I would be engaging in self-deception. There is no justification for stating that I have done my best. All I can say is that it should be good enough.