Frankl's account of surviving Auschwitz and the logotherapy framework that emerged from it. The core idea — that meaning can be found in any circumstance, even suffering — is one of those things that sounds obvious until you realize how few people actually live by it.
The most striking part isn't the Holocaust narrative. It's the clinical observation that prisoners who lost their sense of purpose died faster than those who maintained one. Meaning isn't a luxury. It's a survival mechanism.