I agree that some people may want to see more evidence than others. Of course, there is no clear boundary between "obvious" and "needs proof". However, I found

I agree that some people may want to see more evidence than others. Of course, there is no clear boundary between "obvious" and "needs proof". However, I found that most people are quite able to judge whether it would be helpful to include a source for a statement. I think that within most discoursive communities there is an implicit consensus on when a statement needs an explanation or a supporting source for it to be accepted [1]. Regarding the author's "duty": Maybe I should have called it 'courtesy' instead. On the other hand, if I am not completely mistaken, HN was intended as a forum for constructive and thoughtful low-noise discussions. As I want to profit from these discussions, I personally see it as my duty to make my comments as helpful as possible. I would argue that including source for statements more often is beneficial to a discussion than not. Therefore, I prefer to see sources. [1] sorry, no source but my own experience as a member of some scientific communities and online forums.