a why to live for

"Hat man sein warum? des Lebens, so verträgt man sich fast mit jedem wie?" or "If we have our own why in life, we shall get along with almost any how." - Friedrich Nietzsche “Götzen-Dämmerung; oder, Wie man mit dem Hammer philosophirt” 1889 

As found in Man's Search for Meaning by Viktor Frankl. "There is much wisdom in the words of Nietzsche: “He who has a why to live for can bear almost any how.” I can see in these words a motto which holds true for any psychotherapy."