1st Therapist: Started with an education degree and moved into counseling. Ended up has director of counseling eventually for my university.
2nd Therapist: Started as a theologian and pastor for a major denomination. As he started working with church members, he saw a need for more training and skill in working with members dealing with their mental health needs. He went back to school to add a degree in counselling, etc.
3rd Therapist: He told me the story that he started college as a business major (if I remember right). One weekend, he helped his best friend's mother move from one office to another; she happened to be a psychologist. He started talking to her about it and became fascinated by the topic . . . and the rest was history.