I don’t care who you are, you don’t stay focused for 8 hours straight. Or 4. Not even 2, actually.
Our focus ebbs and flows during the day, in what are called ultradian rhythms.
An ultradian rhythm is a biological cycle that repeats itself within a day. We have many of them, related to our sleep, hormone secretion, heart rate, appetite, etc.
The main point here is that we are very rhytmic creatures. To function properly, we need periods of activity and periods of rest.
After around 90 minutes of focus, you will start to feel tired or distracted.
That’s your cue to take a break, move a little, maybe look at something in the distance to relax your eyes and neck.
If you keep pushing it, you will get more tired and your productivity will suck.
If you do take a break (ideally 20 minutes, but 5 would already be a great start!), you will actually be more productive. You will do more and in a better way.
Every time you think you don’t have time to take breaks because you have too much work, remember that.