Forever green is the tree of life

"All theory is gray, my friend. But forever green is the tree of life."

— Goethe

Rudolf Steiner:  "If one looks but a little into the future those ideas which applied to past and present are already no longer valid. It is most important that people should not consider that something they have once brought into a beautiful concept is a truth for all time. Men must get into the habit of making ideas fluid, of recognizing that ideas change — that will be an advance. The ability of passing over from rigidly dogmatic ideas to mobile ones must be cultivated in those who would be the bearers of the future. For just as times change so must our ideas change too, if we would understand the times."

Source: June 5, 1907. GA 99