It is only when we have experienced the worst, most crushing of times - that we can experience the joys of genuine friendship—

You cannot judge the quality of another's friendship by superficial appearances, especially when things are going smoothly. It is only when we have experienced the worst, most crushing of times—when we have plumbed the depths of life—that we can experience the joys of genuine friendship. Only a man of principle, a woman of resolve—a person who stays true to their chosen path—can be a trusted and true friend, and have real friends in turn.

Wisdom for Modern Life by Daisaku Ikeda 25/1