Frankl was the founder of logotherapy, which is a form of existential analysis, the "Third Viennese School of Psychotherapy". His best-selling book Man's Search for Meaning chronicles his experiences as a concentration camp inmate, which led him to discover the importance of finding meaning in all forms of existence, even the most brutal ones, and thus, a reason to continue living. Frankl became one of the key figures in existential therapy and a prominent source of inspiration for humanistic psychologists.