[oltdaniel]

Because they are recommended or have been explored by a lot of people. Would you buy a product off Amazon without seeing the number of reviews? How do you know it is "quality content".

More votes than comments = something worth reading and seems to be valid content. Less votes than comments = seems to have invalid points with a big dicussion.

HNs "quality index" for each post can be "calculated" by everyone. Without these numbers you don't know these kind of informations. The title of a post should always be in the focus, thats for sure. But thats why it has a larger font.

[2038AD]

With posts, I mostly skim the titles for what looks interesting. I take fewer comments as a bonus but I can't say exactly why (less noise?). I don't look at the votes (though it obviously contributes to what I see).

With books, I mostly read based on individual recommendations (or references). It's more natural to me than going with what's popular though it doesn't exclude it. It has the bonus of being an imperfect quality filter which mixes the good (as determined by people I trust) with the unusual.

To be honest, when I have read books based specifically on popularity I've been thoroughly disappointed. Reading Thinking Fast and Slow was mostly challenging with a mixture of bad examples and bad terminology ("systems 1 and 2"). I enjoyed the book a whole lot more near the end when it was discussing the incompleteness of/problems with economics. Some of my distaste for the earlier parts possibly comes from exposure to critics beforehand (e.g. Gerd Gigerenzer) and to the optical illusions. Similarly Surely You're Joking, Mr Feynman! can be amusing but a lot of the stories boil down to "aren't I clever?".