Working hard ... can mean two things: 1) Someone who works hard without rest. or 2) Someone who works effectively fulfilling their duties but without exceeding their limits of endurance.
As in the post focuses more on the hard work where the individual gives up the last drop of energy to improve their performance, I think the following: This really is counterproductive, you can never fulfill the duties effectively if you force more of what your body can hold, what you do is wear yourself out, fatigue, get tired and therefore every time your efficiency will be lower despite your efforts. Therefore it is necessary to do things calmly, but safely. Plan on activities and time, as you say you have to be smart. It is not always necessary to exceed our limits to improve, sometimes we should only have a good plan where our work does not affect our health in order to give a better performance.
RE: Work hard isn't enough!