A classic from 1929. It’s really hard to find and it costs an arm and a leg to buy (printed scan book is ~$30). It’s short and has some interesting stories, however you’ll get 99% of it by reading my summary below.
Probably all of us have found ourselves finding a solution to a problem when we were not actively thinking about it. We might have gone for a walk, working on a hobby or just went for a shower. This is the subconscious mind at work. When you give it time and relax, ideas start popping up that you haven’t thought of them when you were actively thinking about solutions.
I hoped this book would go into detail on how to do this effectively, however the lesson is just “leave the desk and relax”. Simple, really.
Desks are not thinking machines. Do not plan or think about business when behind a desk. When stuck with a problem, leave it and focus on something else. A solution will come up on its own later. Part of your day, do whatever you want to do, is pleasant and puts the mind at ease.