
Positive Thinking Every Day : An Inspiration for Each Day of the Year (1993), "April 13"
Earlier variant: People become really quite remarkable when they start thinking that they can do things. And those who have learned to have a realistic, nonegotistical belief in themselves, who possess a deep and sound self-confidence, are assets to mankind, too, for they transmit their dynamic quality to those lacking it.
You Can If You Think You Can (1987), p. 84