This post pretty much makes the statement a lot of scientific research has already proven. Your brain needs rest in order to form new neural connections (especially when you're learning). Working long hours to the point where you are experiencing mental fatigue is counterproductive to one's efficiency and overall output. Even for those people who are capable of pulling 12 - 16 hour days their productivity wanes after a certain point and are more prone to producing lower quality work and making errors. https://www.scientificamerican.com/article/mental-downtime/