Productivity momentum throughout the day can be helped along by being proud of what you have done so far and imagining the satisfaction and reward rather than the difficulty of completing upcoming tasks.
When feeling blue about not achieving what you had hoped, the last thing you should do is give into more short term pleasures. Instead try to get some of your easier tasks you have out of the way. This will bring more gratification overall.
And most importantly; when things just haven’t panned out don’t stress about it. High cortisol levels in the body lead to a host of negative health effects, one of which is decreased productivity which compounds the imaginary problem. Really everything we do is to feel good and content, but the belief that we need to DO something to achieve that is only a belief of the human game. We have the choice to interpret life the way we’re persuaded to, as a chore, or for what it is, a ride.