Diseases may be thought to have internal or external causes or sometimes both. According to Cherokee medicine man Rolling Thunder, negative thinking is the most important internal cause of disease. Negative thinking includes not only negative thoughts about oneself but also feelings of shame, blame, low self-esteem, greed, despair, worry, depression, anger, jealousy, and self-centeredness. Johnny Moses, a Nootka healer, says "No evil sorcerer can do as much harm to you as you can do to yourself."