Sometimes we have the intuition that we are not really living, that there has to be something more than just buying stuff, and getting ahead in the "pursuit of happiness" that everybody tells us is the meaning of life.
At least this is what happened to Harry Haller, the main character of Hermann Hesse's Steppenwolf. This deeply philosophical novel, just for madmen, is definitely not for everyone.
From the construction of personality to the worthiness of knowledge, this book smashes everything we thought life was about, ending with a total refreshment of our world view. Simply mind-blowing.