Lee believed to some extent that "I'd rather be overtrained than undertrained". This was regarding to calisthenics, technique training.
I think that if one has the fitness to do it, techniques can be done even when fatiqued.
It should be known, that it is no use to train delicate motions when one is tired, only resistance. This way the coordination does not get off by repeating gross motions. This is commonly known principle of sport science.
Low aim is the highest crime a man has. Self-imposed limits affect your work, morality, everything.