I am also confused by this. I've heard from many different places, and experienced myself I think, that fasting seems to make all your senses sharper and generally makes it easier to focus. And I've heard that this is because when you're hungry it's important in the EEA to get food, and focusing helps towards that.
But then why doesn't evolution just make your senses sharp all the time? The best hypothesis I can come up with is that having such sharp senses is bad or unsustainable over the long term.
In which case you probably shouldn't fast just for the heightened focus. Or maybe not much more than people in the EEA did.
(Another hypothesis is that people were hungry enough in the EEA to basically be in this state of heightened focus all the time. But then why turn it off as soon as you get food in your stomach?)
Huh, so are you talking about attention or willpower? They're not quite the same thing (though you can use willpower to help focus on something).
Checklists are powerful, and I don't use them enough. You probably don't, either.
Below are some of my own checklists. Please share your own!
I don't know how to do X.
I don't understand X.
I feel mentally exhausted but can't afford to sleep right now.
I don't want to get out of bed, but I should.
I'm procrastinating on task X.
I'm about to send an email / post a comment of some significance.
(I don't do these ones nearly enough! D'oh!)
I feel sad about not doing a better job at X.
I'm about to make a decision of some significance.
I could go on, but... what are yours? (Now is also a good opportunity to make some checklists for yourself, based on what you think tends to work for you.)