I read a great article the other day about how Navy Seals are trained to ignore their body's signals for pain, because in reality muscles can be pushed a lot harder than when the safety signal goes off. The article also mentioned a seal who did a marathon and ended up breaking his foot because he ignored his pain signals. It doesn't even seem to be an uncommon thing with pro-athletes. If you've got a strong mind then you can force yourself to endure things that are not healthy to endure in the long term.
Yesterday my co-workers and I kicked off an exciting new thing, and we spent several hours thinking of a technical design for what we're going to program. When the day ended there were still things left undone so I felt excited (at first) to work a little more on the idea to get some important bits fleshed out. As time went on that excitement dissipated, but I forced myself to continue anyway because I was nearing the end. I managed to get a lot done before I went home, but in the evening some of the problems were still stuck in my head, and I found it hard to stop thinking about them.
Today I went to work at the usual time, did all the usual things, and continued deeper into the new idea. But at around 3 o'clock my brain just.. stopped. I ceased to be able to solve problems or find creative solutions to things. I tried forcing myself again to do a little bit more, but the results were not as effective as yesterday. I think I've reached a point where it's just not useful to try to do more. I don't think that forcing myself to work longer trains my brain to be more effective for a longer period of time. I've tried that for over 10 years now, and it just does not work. When my brain runs out of energy then the best thing to do is to just stop, walk away and do something else. Passive entertainment or a braindead session of Minecraft usually does the trick of keeping my mind occupied without feeling bored. But when the energy's gone I just don't feel like doing much else.
It seems much easier for me to hit my mental limits than it is to hit my physical limits. During cycling trips there were a few moments during which I really just felt all my muscle strength disappearing, and the only thing I could do was stop and have a snack before I could go on. But those moments were quite rare, whereas I hit my mind's limits just about every other day at work. It seems like my mind is permanently limited to under 7 hours of useful time when I'm at max capacity. the obvious thing to do is to not push myself so much and spread out the workload a bit more, which in the end is probably more productive. Sometimes you can't avoid getting fired up for a problem though. Next time I'll try to spread out my mental load a bit more. Pacing is key. Sustainability improves satisfaction.