I know if I'm going to have a shitty day or a great day the moment I wake up, the first interaction I have with a person (knowing this may make it more likely to happen, but short of that...).
I know when my brain is running on all cylinders, and when it's choking for more air. Tuning into these signals (I have no idea what they are, only 'feelings'), I can lay out the things I want to do in the next few days, and roll with the punches. It'd be interesting to see the amount of time idlers and time progressors (I'm at my computer most of the day, looking at my google search history would give a good indication - I generally don't google that much when I read articles on HN or Reddit, but when I'm doing something I'm googling up a storm).
No sense fitting a square key into a round hole when tomorrow the round key will be sitting in my hand.