Peopleware: Productive Projects and Teams

https://www.goodreads.com/book/show/67825.Peopleware

Happy and healthy teams result in productive teams, who would have thought :)

Some of my best work was done during 40 hours weeks or less. Whenever I break that rule the end result suffers because I lose creativity and focus.

It's ok to do the occasional extra time when you're really engrossed in what you're doing, but overwork has long-term negative effects.