Reading The Subtle Art of Not Giving a F*ck, I noticed that non-fiction best-sellers are often adapting old wisdom to modern times. Manson's book is a modern take on stoicism, for example. If you read Marcus Aurelius and Seneca, you'll already get the core message of the book.
Stephen King also proposes that writers have to be readers.
Combining those two statements, I think it's important to know your classics. That's how Renaissance Humanism started, by studying the problems that have been formulated and answered for centuries.
Reading the latest books isn't without worth, but perhaps it is wiser to start at the beginning of humanity. Or at least, try to balance the old and the new to get a sense of the bigger picture.
I currently have three books I want to summarize for Sipreads: Thoreau's Walden, Seneca's On the Shortness of Life, and Montaigne's Essays. I choose those books because I want to integrate my findings in my upcoming book: Walden is among the precursors of minimalism, Seneca's essay urges its readers to spend time more carefully, and Montaigne's Essays laid the foundations of Humanism. Each proposes interesting principles to live one's life, and since Alter-Nomad is about defining a lifestyle, it makes sense to refer to them.
I'm only frustrated by the fact there isn't enough time in the world to read every classic.