As a rule, I only write stuff if I feel like I have an opinion or take on something that isn't very common. I've abandoned half-written posts because I realized that I am not saying anything particularly unique or interesting, and I don't really see the point of writing about it.
Granted, being uninteresting has never really stopped me from writing long comments on HN...
Granted, being uninteresting has never really stopped me from writing long comments on HN...