“Remember that sufferings like medals have also a reverse side and ponder over the words of blind Helen Keller" Although the world is full of sufferings, it is full of the overcoming of it."”

Theodore Zeldin in An Intimate History of Humanity (1994) This quote seems to obviously refer to Helen Adams Keller, but why she is referred to as "Mary Helen Keller" is not clear.
An Intimate History of Humanity (1994)

Optimism (1903)

From "Persönliche Notiz", in the recital program for the opening event of festival year "100 days, 1700 years – Jewish life in Darmstadt". https://www.darmstadt-tourismus.de/en/visit/events/events/artikel/detail/juedisches-leben-in-darmstadt-festjahr-100-tage-1700-jahre.html Liedgut – Famous Musicians of Jewish Origin (2021), p. 2 http://web.archive.org/web/20210902070031/https://staatstheater-darmstadt.s3.eu-central-1.amazonaws.com/produktion/programmbuch/994?response-content-disposition=inline%3B%20filename%3D%22210831_PH_Liedgut_web.pdf%22&response-cache-control=public&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAUCI3T77LT4YWGJ7O%2F20210902%2Feu-central-1%2Fs3%2Faws4_request&X-Amz-Date=20210902T070031Z&X-Amz-SignedHeaders=host&X-Amz-Expires=600&X-Amz-Signature=d36591acd16fc78b29808a50bfaf03d75dc5d97aaab1945548d8ad24040d4a9d.
Original: (de) Jüdische Geschichte ist voll von Leiden und schrecklichem Kummer. Aber sie ist auch voll von unermesslicher Freude. Wir ehren das Leiden durch Erinnern. Wir ehren die Freude durch Feiern.

As quoted in "10 questions for Lance Armstrong" by Bill Saporito in TIME magazine (28 September 2003) http://www.time.com/time/magazine/article/0,9171,1005777,00.html
Context: I'm not happy if I'm not doing some physical suffering, like going out on a bike ride or running. First, it's good for you. No. 2, it sort of clears my mind on a daily basis. And it's a job. My job is to suffer. I make the suffering in training hard so that the races are not full of suffering.

Source: Book of Longing

On ne guérit d'une souffrance qu'à condition de l'éprouver pleinement.
Source: In Search of Lost Time, Remembrance of Things Past (1913-1927), Vol. VI: The Sweet Cheat Gone (1925), Ch. I: "Grief and Oblivion"