Anxiety
The philosopher Søren Kierkegaard, in "The Concept of Anxiety" (1844), described anxiety or dread associated with the "dizziness of freedom" and suggested the possibility for positive resolution of anxiety through the self-conscious exercise of responsibility and choosing. In "Art and Artist" (1932), the psychologist Otto Rank wrote that the psychological trauma of birth was the pre-eminent human symbol of existential anxiety and encompasses the creative person's simultaneous fear of – and desire for – separation, individuation, and differentiation.
George Humphrey (psychologist)
In 1951, he wrote "Thinking: An Introduction to Its Experimental Psychology", which had considerable success as it provided a written description of all research done on mental problem solving in humans conducted by Otto Selz, the Würzburg School, and other Gestalt psychologists. Their findings largely supported Humphrey's assertion—discussed in his book "Directed Thinking" (1948)—that a sequence of thoughts is governed by motivation.