[renaissance_tea]

This is asked pretty often. I think I’d say the act of reading books consistently and reflecting on the ideas as a habit is what makes you smarter, not just a single book. Fiction and nonfiction alike.

But to be less pedantic and answer your question. Deep work and why we sleep are both amazing books. They contribute to making you smarter by improving aspects of your life

[lifeplusplus]

This. Id add reading more nuanced thoughts. Sometimes it's a research, a book, a blog, Wikipedia article, ..