The word 'attack' is probably the confusing bit here, and it's not essential. The point is, if you start to comment on someone personally, e.g. about their motivations, in the context of a disagreement, it's almost certain to provoke the other person further and lead to a negative spiral. To prevent HN from being taken over by ill feelings, we all need to have the discipline not to react that way, even when another commenter is wrong or provocative.

https://news.ycombinator.com/newsguidelines.html