I notice that, when it comes to big ideas, the writers who get read a lot are rarely the first to think of these big ideas. For example, C S Lewis is super popular, he says a lot of good things, but he has very few original ideas. This is a good thing! He effectively expresses a lot of important ideas, bringing together the thought of some of the most important thinkers. Anyone would have floundered if he was relying only on his own thought, even Lewis.
It is funny how often people that I've talked to think that Lewis came up with, say, the Trilemma, when he didn't.
This is unhealthy: it's easy for our culture to lose sight of the notion that thinking is an ancient tradition. If we see Lewis' thought as basically modern, we're actually doing injustice to what he says, because, while he has a modern worldview, he is so deeply influenced by premodern thinkers, who have timeless things to say. This is dangerous! We are so inclined to regard modernity as qualitatively better than the past, and use this as an excuse to dismiss antiquity.
I would like to see someone write a blog that lists the big influences on individual books.