Which is the most difficult to learn, Tianji, Diji and Renji?

Celestial pole (Yijing, Wei Zi Dou Shu); Human body discipline (including acupuncture, Huangdi Neijing, Shennong Herbal Classic, Treatise on Febrile Diseases, Synopsis of the Golden Chamber). All his teaching videos are based on his own life experience, telling several classic works of traditional Chinese medicine in simple terms, which even Xiao Bai of traditional Chinese medicine can understand.

Ni was a traditional Chinese medicine practitioner in the Han and Tang Dynasties, and was known as the "Five Meetings". He once served as a member of the Supreme Committee of the Chinese Medicine Committee of the Florida Ministry of Health, and was in charge of all related businesses such as doctor qualification, license renewal, and physician re-education plan.