
""Siddhartha" is a 1922 novel by Hermann Hesse that deals with the spiritual journey of self-discovery of a man named Siddhartha during the time of the Gautama Buddha. The book, Hesse's ninth novel, was written in German, in a simple, lyrical style. It was published in the U.S. in 1951 and became influential during the 1960s. Hesse dedicated the first part of it to Romain Rolland and the second part to Wilhelm Gundert, his cousin.The word Siddhartha is made up of two words in Sanskrit language, siddha (achieved) + artha (what was searched for), which together means "he who has found meaning (of existence)" or "he who has attained his goals". In fact, the Buddha's own name, before his renunciation, was Siddhartha Gautama, Prince of Kapilavastu. In this book, the Buddha is referred to as "Gotama""
Half-time: to think what-the-hell-comes-next (only if you are 40+)(it won't resonate with a 20yo)
Systemantics, Nexus: if you work in mega-big-corpos this will save your life
Hold on to your kids, The anxious generation: if you got kids
Strong Fathers Strong Daughters: (and mothers/sons) if you got kids (too Christian-y for my taste but an amazing 'manual' to manage the relationship with your kid(s))
1984, Animal Farm, Gulag Archipelago: ...
Light on Yoga: (also do practice yoga, it's good for most-if-not-all)
You asked for "one book"... but.. life.. is not 'one' thing. Systemantics (and Dilbert) have helped me stay afloat at work. Siddartha gave me a perspective in live about myself, the different 'people' I have been throughout my life.All the listed ones are books I read and read again every few years. They shaped me the first time I read them, keep me 'grounded'/taking stock/thinking the 'change' in me and my life. I see them as a 'check-diff' and how I have changed/evolved/devolved since the last time I read it/them.
„Getting Things Done“ by David Allen. Learned about how to capture everything that’s on my mind and organize it. Best way to keep sane. - Also how important it is to contantly review my systems and lists to keep them current and to make decisions.
„Structure and Interpretation of Computer Programs“ by Abelson / Sussman. Learned a lot about how to structure and organize code, how to abstract and build smaller functions that solve problems and glue them together and thus build ever more complex soltions.
„Siddartha“ by Hermann Hesse. Reminded me of my inner struggle in my young years regarding life, religion and meaning of life.
„Wherever you go, there you are” by Jon Kabat-Zinn. Introduced me to the idea of mindfulness, of being present, of letting go.
To those who mentioned Marcus Aurelius's meditations, I recommend the reading of "Zen mind beginner's mind". Along the same lines of somewhat spiritual books, "Siddartha" is a classic and also Khalil Gibran's "The Prophet".
Very different: for my personal history, reading "Goedel, Escher, Bach" when I was 18 deeply affected my vision of things. Other science books I loved: "the unfolding of language" (historical linguistics) and "the world within the world" (physics and philosophy of physics).
For something much more recent, that changed my view of the contemporary world, I recommend "Factfulness" by Hans Rosling. It's about understanding "poor" countries in their variety and in a less stereotyped way, but especially about understanding that living conditions across the world, essentially without exception, have massively improved over the last century. I feel Rosling's is only part of the story, though, and "Sapiens" (mentioned by others below) tells parts of the other half.
I also like poetry, and in the rare occasions I am in the right frame of mind and focus to read poetry, it feels like a powerful meditation or prayer.
If you want to "expand" your vision of things, one thing I tried to do, and loved, is reading as much as possible books from other cultures, for example postcolonial literature. I particularly liked Chinua Achebe's "things fall apart". Somewhat related, "the moon and the bonfires" was deeply moving to me, the life of a man in agricultural Italy after ww2. The reason why I put these together is that they do something extraordinary: we are used to descriptions of africans during the colonization process, or of poor Italians after the war, but we are not very used to them being full three-dimensional characters, people like us, and stepping in their shoes.
Finally I enjoy travel books, for similar reasons. Among my favourites is "the road to Oxiana", written in the 1930s, and full of british humour. Also, Rory Stewart (british politician, diplomat and academic) walked Afghanistan in 2002 and told the story in "The places in between". Very, very helpful for understanding Afghanistan beyond the news.
I could go on forever!
I prefer a book like Siddartha by HH. The lessons are there, but the interpretation is open and the narrative is not compromised. You start reading it and you don't want to stop reading it because you're now part of Siddharta's journey. You’re no expecting the punch line that has the lesson, you simply live the story and therefore live the lesson.