Just as valuable energy is wasted by spending time on activities that are of no value, energy can be wasted on loose thinking.
Imagine that your mind has an energy measure of 1000 watts at its disposal.
Each time your mind wanders off the project at hand, to a nagging worry, to all the things to do by the end of the day, 100 watts is lost.
Quite soon the entire energy supply is gone.
This is the nature of the mind.
Fail to discipline it and your energy levels will be depleted and your accomplishments will be minimal.
Control it and you will see great things happening.
You will feel more powerful and achieve difficult tasks with ease.
The 19th century philosopher Henri Frederic Amiel summed it up nicely: “for purposes of action, nothing is more useful than narrowness of thought combined with energy of will.”