Not so much of a question but a request, Where can I find information on a philosopher who has a
theory on why we become stronger after adversity or hard times?
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Answer: Try the Stoics, e.g. Seneca, Marcus Aurelius.
Also, try Boethius's Consolation of Philosophy.
Nowadays, try anything written against the psychotherapy profession, especially anything written by
Frank Furedi.
Richard Craven
How about Nietzsche (Twilight of the IdolsMaxims and Arrows):
"From the military school of life.— What does not kill me makes me stronger."