"It all dates from those summers alone in the high desert, me lying on my belly and watching wild horses with my binoculars for hours at a time. Straining to see in the moonlight, striving to fathom mustang ways, I knew instinctively I had chanced upon something important but could not know that it would shape my life. In 1948 I was a boy of thirteen learning the language of horses. . . ."
He wrote that by personally observing horses in the wild, he learned to "listen" to their non-verbal "language"; that when horses understood that they can trust you, they will decide to be with you. Roberts registered as his term for "hooking on", the phrase "Join~Up", in which a trainer negotiates with an untamed horse to form a voluntary relationship with him