I don’t think productivity ever increases with contiguous time spent on a given activity, at least in the short term. (Yes, longer term you can identify and implement working patterns that increase overall productivity.) All the effects push in the opposite direction: low hanging fruit gets picked first, you get tired, you get hungry, you’ve done all you can on your part of the critical path and need to wait for others to do their bit before you can continue, etc.
So I think there are two explanations here if someone on Hacker News does claim that the last hour is the most productive. The first is post-rationalisation, i.e. if you have been working crazy 99 hours straight on something you’d better conjure up some pretty convincing-to-you-sounding reason to work the 100th hour. The second is that you are falling for a perceptual trick: let’s say you’re working 99 hours straight on finding a difficult bug, and in the 100th hour you fix it. You can say “wow, that 100th hour was clearly the most productive, because in the first 99 hours I didn’t solve the bug and in the 100th hour I did”. But that’s not what productivity means. What is actually happening is you are making slower and slower progress during the 100 hours but still eventually get there.
Personally I have found that judging my position on the curve is pretty easy, if you are mindful and deliberate about doing that continually. This mindfulness and deliberation doesn’t seem to happen automatically, though, which makes it difficult if you don’t do that.
I don’t think productivity ever increases with contiguous time spent on a given activity, at least in the short term. (Yes, longer term you can identify and implement working patterns that increase overall productivity.) All the effects push in the opposite direction: low hanging fruit gets picked first, you get tired, you get hungry, you’ve done all you can on your part of the critical path and need to wait for others to do their bit before you can continue, etc.
So I think there are two explanations here if someone on Hacker News does claim that the last hour is the most productive. The first is post-rationalisation, i.e. if you have been working crazy 99 hours straight on something you’d better conjure up some pretty convincing-to-you-sounding reason to work the 100th hour. The second is that you are falling for a perceptual trick: let’s say you’re working 99 hours straight on finding a difficult bug, and in the 100th hour you fix it. You can say “wow, that 100th hour was clearly the most productive, because in the first 99 hours I didn’t solve the bug and in the 100th hour I did”. But that’s not what productivity means. What is actually happening is you are making slower and slower progress during the 100 hours but still eventually get there.
Personally I have found that judging my position on the curve is pretty easy, if you are mindful and deliberate about doing that continually. This mindfulness and deliberation doesn’t seem to happen automatically, though, which makes it difficult if you don’t do that.