The meaning of this sentence is that a person's fate is not decided by heaven, but controlled by himself. As long as we can strengthen our faith and practice hard, we can change our destiny and achieve longevity and happiness.

This sentence comes from the Taoist classic "Five True Chapters" and is one of the important contents of Taoist health preservation. It emphasizes the importance of people's subjective initiative in shaping their own destiny, and holds that people can achieve eternal life and happiness through their own efforts and practice.

"My life" in this sentence refers to a person's life and destiny, and "returning Dan" refers to the cultivated Dan medicine. The whole sentence means that if a person can enhance his vitality by practicing Dan medicine, then his life can be prolonged and he can have a longer and happier life.