We try to draw the line according to principles that I've explained many times over the years. If you scroll back through the comments, for example, at https://hn.algolia.com/?dateRange=all&page=0&prefix=false&so..., you'll find them. If you read some of those and then still have a question that isn't answered there, I'd be happy to take a crack at it.
Btw, I'm not claiming that we make every individual call correctly - that's an undecidable question anyhow since everyone will have their own evaluation of "correctly". But at the more general level of what principles to apply, I do think there's a certain consistency: they've been the same for many years, and we do our (fallible) best to follow them.