I, personally, have diminishing (or negative?) returns to my creative work as I explicitly work on a problem past some amount of time. I often have insights coming to me out of nowhere while I’m relaxing or enjoying hobbies on nights or weekends.
Whenever one considers innovative endeavors and their productivity, one must consider that innovation is fundamentally wasteful. The problem with innovation is not about how to get as much of it for as little of a cost as possible. It is to get innovation at all. By optimizing your production function, you risk losing all of it. I sooner blame someone for his publication list being too long than being too short, said Dijkstra.
My view is that we tend to underestimate “intellectual latency”. There is a delay between the time you approach a new idea and the time you have fully considered it.
Thus our brains are not unlike computers. Your processor might be able to run at 4 GHz and be able to retire 4 instructions per cycle… but very rarely are you able to reach such a throughput while working on a single task. The productive intellectuals that I know tend to work on a few ideas at once. Maybe they are writing a book while building a piece of software and writing an essay.
So you should not focus on one unique task in the hope of finishing it faster. You may complete it slightly faster if you omit everything else but the sum total of your productivity might be much lower.
There is also a social component to human cognition. If you hold on to a problem for very long, working tirelessly on it, you may well deprive yourself of the input of others. You should do go work and then quickly invite others to improve on your work. No matter how smart you think you are, you cannot come close to the superior ingenuity of the open world.
Energy and sanity are essential ingredients of sustain intellectual productivity. Hammering at a single problem for a long time is both maddening and energy limiting. Our brains are wired to like learning about new ideas. Your brain wants to be free to explore.
And finally, the most important reason to limit the amount of work you invest on a single task is that it is a poor strategy even if you can do it with all the energy and intelligence in the world. Sadly, most of what you do is utterly useless. You are like an investor in a stock market where almost all stocks are losers. Putting all your money on one stock would ensure your ruin. You cannot know, at any given time, what will prove useful. Maybe going outside and playing with your son sounds like a waste of your potential right now, but it might be the one step that puts your life on a trajectory of greatness. You want to live your life diversely, touching many people, trying many things. Learn to cook. Make cocktails. Dance. Go to the theatre. Play video games. Write assembly code. Craft a novel.
Many years ago I started to blog. I also started publishing my software as open source in a manner that could be useful to others. I started posting my research papers as PDFs that anyone could download. None of these decisions seemed wise at first. They took time away from “important problems”. I was ridiculed at one point or another for all of them. Yet these three decisions ended up being extremely beneficial to me.
Further reading: Peer-reviewed papers are getting increasingly boring