- Peterson, Seligman, and Valliant (1988) : Peterson, Seligman, and Valliant Psychologists who in 1988 studied Optimists and Pessimists. The three (3) suggested that Pessimists tended to explain setbacks in their lives as the result of things within their personality that were unchangeable. In contrast, Optimists tended to explain setbacks as the result of things arising from situations within their control, but which were not their own fault.