There was a time a dozen years ago when I was working alone on my (over-elaborate, uncontrollably sprawling) graphics software product. One time I wrote a multi-thousand-line refactoring of existing code into a new class and felt very happy about getting it done. The next day I discovered that I had already done the exact same work the previous week, just as a slightly differently named class.

That wasn’t an isolated memory loss experience in those days. I ordered lunch, sat down, then five minutes later just stood up and left, assuming I’d already eaten. An hour later I realized what happened.

Long-term productivity is impossible without proper rest, including regular vacations where you’re truly out of work mode preferably for a week at the minimum.