I've always loved the concept of "gumption":
"gumption: noun [ U ] UK /ˈɡʌmp.ʃən/ US /ˈɡʌmp.ʃən/ informal
the ability to decide what is the best thing to do in a particular situation, and to do it with energy and determination."
Always, "a particular situation" includes your mental state: tired, enthused, confident, preoccupied.
You don't start building IKEA furniture at the end of a frazzling day, for example.
This is why self-determining workers can be so productive but not seem to be grinding away all the time--you do the tricky creative stuff when it flows smoothly, and do paper-shuffling when you're all out of juice.
You can deliberately feed your gumption with confidence and enthusiasm-building stuff. Sports coaches do this--why not do it an all areas of life?
Anyway, gumption is a great concept and helps to shape good use of time. Thank you Robert M. Pirsig and the book "Zen and the Art of etc. etc.", which is where I got it from.