The book has harsh critics. I read it and I think much of sees truth, though it also a book of another era -- an era in which "man" more or less included women.
Today psychology, psychiatry, neurology and the sciences retain little of Frankl's life work. He could not grasp that meaning might exist in the absence of religion, or that responsibility could be assumed rather than fundamental. I believe, however, that he had a true understanding of the extremes of human nature for evil and for good.
YouTube (and the Ted site) have a video of a lecture he gave later in his life. From the Frankl Institute (with let another video copy!):
YOUTH IN SEARCH OF MEANING, 1972 [4:22]Frankl speaking at the "Toronto Youth Corps" in 1972. See Frankl "at his best" as he vividly explains his theories, and even draws analogies to piloting an aircraft – a passion he had recently picked up.
In this lecture he talks about how one must "crab" an airplane to adjust for a crosswind (1:45). To reach a destination you have to periodically turn into the wind. He expands the analogy to people:
If we take man as he really is we make him worse. But if we overestimate him ... if we seem to be idealist and are overestimating ... overrating man ... and looking at him up high ... we promote him to what he really can be...
... Do you know who has said this? If we take man as he is we make him worse, but if we take man as he should be we make him capable of becoming what he can be? ... This was not me. This was not my flight instructor. This was Goethe.
From this it is a small Google step to the Goethe quote (in English):
When we treat man as he is we make him worse than he is.When we treat him as if he already was what he potentially could be we make him what he should be.
In the strange time of June 2020 I think this is worth remembering.