Rest gives us a clear mind.
A clear mind can think well.
When we think clearly, we make well-thought plans and reduce the need to hustle. Because hustle often is a result of lazy thinking and not planning how one can do something efficiently.
Clear thinking also helps us realize which part of our input is creating maximum output. With this insight, instead of working 14 hours on mostly non-impactful action, we can work 4-5 hours of things that will create maximum impact.
And, when we work for a small amount of time, we are able to work with a clear head and achieve even better results than if we worked for long hours with a tired brain.