While I respect your opinion, I think that there are a large number of people who struggle with the feeling of not having accomplished anything / not being "good enough" even in be face of what most would consider career success.
Psychology has some terminology for this: cognitive distortions, and in particular, minimization and magnification. Whether it's due to upbringing, environment, what have you, some large number of people tend to discount their successes and zero in on whatever they see as their flaws or failures.
The field of CBT is one way to work with this. I particularly like the book "Learned Optimism" by Martin Seligman, which talks about how the stories we tell ourselves about success and failure lead to happiness / optimism or depression / pessimism. He also talks about some of the research that's been done to help change peoples' explanatory style.
This + meditation has been helpful to me, as well as trying to take other peoples' positive feedback to heart more, rather than discounting it as politeness.
Also, although I think it can be helpful to produce things, I feel like your advice can feed into the story of "not doing enough," even if they are. There probably are some people who feel this way because they're actually not doing much, but I feel like a lot of the people on this site are more likely to be the types with unrealistically high standards whose problems are not their output, but their perception of their output.
On that note, spending less time on HN and more time with friends / family / doing other things you enjoy can also be helpful, as it helps to diversify your identity.