Pragmatic: when hearing praise, my thoughts are sometimes, "yeah, yeah, cut to the chase." I guess you gotta read your audience.
Emotional: It IS easy to be negative. We also tend to over-experience/over-perceive the negative, which (partially) is how we get over-reaction to criticism or advice, even when asked for. And sometimes we really just want validation. I guess you gotta, uh, read your audience.
This is something I am trying to do in real life as well (although I don't always succeed). For some reason it's really easy for me to open my mouth to talk about weakenesses/problems with things, but it's not as natural to highlight the positive aspects. I also try to say aloud my positive thoughts about people when they pop in my head instead of keeping them to myself.
As an aside, I don't read HN that way. Even when there's a pessimistic tone, I often read right through it and think to myself "that's some good advice". It will be interesting to see whether we become more bearish simply due to the COVID-19 environment we're all working in now.