What is the German original of the "I have come to the frightening
conclusion..." text of JW v Goethe? 

The full text: 
"I have come to the frightening conclusion that I am the decisive
element. It is my personal approach that creates the climate. It is my
daily mood that makes the weather. I possess tremendous power to make
life miserable or joyous. I can be a tool of torture or an instrument
of inspiration, I can humiliate or humor, hurt or heal. In all
situations, it is my response that decides whether a crisis is
escalated or de-escalated, and a person is humanized or de-humanized.
If we treat people as they are, we make them worse. If we treat people
as they ought to be, we help them become what they are capable of
becoming."

Please note that this quote is also attributed to Dr. Haim Ginott. As
a native speaker of German, I could not find any evidence that Johann
Wolfgang von Goethe has written it.

Scriptor

Thank you for your comment Scriptor. I did come across mentionings of
this quote by Ginott as well. And was myself fruitless in searching
Goethe's works in German. But then... there is a lot to search :)