I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection.  

The man who lets a leader prescribe his course is a wreck being towed to the scrap heap.

The greatest thing you'll ever learn is just to love and be loved in return.

The person who tries to live alone will not succeed as a human being. His heart withers if it does not answer another heart. His mind shrinks away if he hears only the echoes of his own thoughts and finds no other inspiration.