He just knew he had to dig deeper to find the core motives behind people's behavior.
Hartman is the founder of "The Color Code" personality theories.
His first book, which he had no inclination to write and the manuscript for which was left behind in an airport for a week, has influenced millions of people.
Hartman began thinking about the field of psychology while serving a Mormon mission.
As a missionary, he found that he loved people and wanted to help them resolve their relationship problems.
Later, as a practicing therapist, he knew that the behaviorism that dominated the field of psychology in the 1970s didn't go far enough to effectively help him treat his clients.
Hartman concluded that all people are born with one of four personality types, to which he assigns a color. "Reds" are motivated primarily by power, "Blues" by intimacy, "Yellows" by fun and "Whites" by peace.