Man's Search for Meaning, by Victor Frankl, is one the great books of the past century.
Frankl (1905-1997) was an Austrian psychiatrist who developed a style of therapy which he called "logotherapy," a style which focuses upon the identification and nurturance of meaning as a primary therapeutic goal. While this style affirms the importance of symptom relief, it focuses on the idea that meaning is available even in the context of extreme unremitting symptoms or suffering.
The gravity of his ideas must be taken very seriously, because of Frankl's own personal experience between 1942-1945: he survived almost three horrific years in Nazi concentration camps including Auschwitz and Dachau. His parents and wife were killed in the concentration camps, and his only surviving immediate relative was one sister. So Frankl approaches these questions with the perspective of one who understands the extremity of suffering, profound loss, and domination by oppressive forces outside of one's control. In this way, Frankl has a deep empathic understanding of what it can be like to experience severe, torturously unremitting psychological illness.
The first half of Man's Search for Meaning is a description of life in the concentration camps. The second half is a brief description of the author's meaning-based psychotherapy style.
As a style issue, I do wish there was more attention to gender-inclusive language, as humans are always referred to as "man," and the pronoun "his" is always used instead of "her." But this is a very small complaint, given the profoundly moving, inclusive, and life-affirming nature of this writing.
This is another of the books I've read recently, which I really ought to have read 20 years ago...