Man's Search for Meaning
Written by a Holocaust survivor and psychiatrist. The argument: meaning, not happiness, is what keeps people alive.
The first half is Frankl's account of surviving Auschwitz. The second half introduces logotherapy — his therapeutic framework built on the premise that humans can endure almost any "how" if they have a "why." The book is short, dense, and permanently changes how you think about suffering and agency. One of those books that gets truer the more life you've lived.