— Alfred Adler 1870 - 1937
En inglés: «It is the individual who is not interested in his fellow men who has the greatest difficulties in life and provides the greatest injury to others. It is from among such individuals that all human failures spring».
Fuente: Carnegie, Dale. How To Win Friends And Influence People. Editor Arthur R. Pell. Edición reeditada, revisada. Editorial Simon and Schuster, 1982. ISBN 9780671723651, p. 55. https://books.google.es/books?id=0KYWs7EdKYMC&pg=PA55&dq=It+is+the+individual+who+is+not+interested+in+his+fellow++spring&hl=es&sa=X&ved=0ahUKEwiNp92Y4bvgAhVI1uAKHQKvCZkQ6AEIKDAA#v=onepage&q=It%20is%20the%20individual%20who%20is%20not%20interested%20in%20his%20fellow%20men%20who%20has%20the%20greatest%20difficulties%20in%20life%20and%20provides%20the%20greatest%20injury%20to%20others.%20It%20is%20from%20among%20such%20individuals%20that%20all%20human%20failures%20spring&f=false En Google Books.