The source is an excerpt from Brian Tracy's book, "The 21 Success Secrets of Self-Made Millionaires." The book examines 21 principles that Tracy believes lead to financial success. The excerpt delves into each of these principles in detail, providing practical advice and action exercises to help readers apply the concepts to their own lives. The book emphasizes the importance of developing key habits, like goal setting, self-discipline, and continuous learning, along with fostering positive attitudes like a commitment to excellence and a willingness to serve others. Tracy argues that through dedication, hard work, and the application of these principles, anyone can achieve financial independence.