“Change is the end result of all true learning.”

Address at Princeton University, "The Educated Citizen" (22 March 1954).
Variant: It is not the years in your life but the life in your years that counts.
"If I Were Twenty-One" in Coronet (December 1955).
This has also been paraphrased "What matters most is not the years in your life, but the life in your years" and misattributed to Abraham Lincoln and Mae West
Context: All progress has resulted from people who took unpopular positions. All change is the result of a change in the contemporary state of mind. Don't be afraid of being out of tune with your environment, and above all pray God that you are not afraid to live, to live hard and fast. To my way of thinking it is not the years in your life but the life in your years that count in the long run. You'll have more fun, you'll do more and you'll get more, you'll give more satisfaction the more you know, the more you have worked, and the more you have lived. For yours is a great adventure at a stirring time in the annals of men.

(X.6) Del Rey, p. 380
Blade of Tyshalle (2001)

Speak French with Michel Thomas, Disc 1

Part I, Ch. 2 : The Evanescence of Evil, § 1
Social Statics (1851)
Context: All evil results from the non-adaptation of constitution to conditions. This is true of everything that lives. Does a shrub dwindle in poor soil, or become sickly when deprived of light, or die outright if removed to a cold climate? it is because the harmony between its organization and its circumstances has been destroyed.

Attributed

Source: The Shadow of the Wind

Source: Don't Sweat the Small Stuff ... and it's all small stuff: Simple Ways to Keep the Little Things from Taking Over Your Life

Source: 1930s, Principles of topological psychology, 1936, p. 218, as cited in: Granville Stanley Hall, Edward Bradford Titchener, Karl M. Dallenbach (1937) The American journal of psychology. Vol. 50, p. 374.