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Any practitioner of medicine must have a general knowledge of ancient and modern history, roughly uphold benevolence and righteousness, abandon the desire for fame and profit, and dedicate themselves to the aspiration of widely providing aid. In this way, one's understanding will naturally become clear, and spiritual assistance will come; why then worry about seeking fame or scrupulously pursuing profit? If not, how could one avoid the shame of Jiang Fu for seeking reputation, or even suffer the fate of Hua Tuo who was executed due to his arrogance in skill?

Regarding the Five Classics and Four Categories (Confucian classics and various schools of thought), as well as military and state ceremonial attire, if there are deviations in their explanation and use, it is merely considered inappropriate conduct. However, regarding medicinal decoctions, even a slight error can endanger life. Should not rulers with chariots numbering in the thousands and leaders possessing wealth worth a hundred gold pieces reflect deeply and act with caution? In the past, the Crown Prince of Xu was charged with regicide because he did not taste the medicine before serving it; when Ji Kangzi offered medicine, Confucius expressed hesitation ("wei da," indicating reluctance to accept without full understanding). This demonstrates that medicine and drugs should never be taken lightly. During the Jin Dynasty, scholars wishing to correct the *Zhouyi* (Book of Changes) and various medical prescriptions first debated them with Zu Ne. Although differences in classics may exist, they do not harm moral teachings; however, ignorance of even minor details in decoctions can determine longevity or premature death, causing significant harm to future generations. How can such matters be judged lightly? Zu Ne's words serve as a model of benevolent wisdom and a worthy mirror for reflection. (From *Yi Shuo*)

Alas! Medicine is indeed difficult to describe! Human life circulates in harmony with the Qi of Heaven and Earth. If nourishment is managed correctly, all things proceed smoothly, and pathogenic factors are expelled; but if nourishment is neglected, internal injury from the Seven Emotions (joy, anger, worry, thought, grief, fear, fright) and external contraction of the Six Qi (wind, cold, summer heat, dampness, dryness, fire) will give rise to disease. The physician treating it must examine both its root and branches. If it is an excess condition, reduce it accordingly; if it is a deficiency, tonify it accordingly. When Yin is peaceful and Yang is secure, one naturally finds comfort in the middle state. Crude practitioners often fail to understand this, leading to "excess reinforcing excess" and "deficiency reinforcing deficiency," damaging what is insufficient and adding to what is already excessive. Consequently, few patients recover. This is the first difficulty.

The movement of Qi and Blood must be guided by meridians. The left and right hands and feet each possess three Yin and three Yang channels. Why, given Taiyang and Shaoyang, is there also Yangming? It takes the meaning of "two Yangs combining to illuminate." Why, given Taiyin and Shaoyin, is there also Jueyin? It takes the meaning of "two Yins intersecting and ending." Which meridian is diseased? What prescription should be used? Treatment itself is not difficult, but one must know the guiding herbs (herbs that guide other medicines to specific meridians). Following this method ensures no disease remains uncured. Crude practitioners, failing to distinguish the Twelve Meridians, apply treatments indiscriminately. This is like trying to catch sparrows in a river or fish in a forest; even if successful by chance, is it logical? This is the second difficulty.

Annual climatic influences vary, so therapeutic approaches must differ. Regarding ascending, descending, floating, and sinking, we follow and accommodate them; regarding cold, heat, warmth, and coolness, we counteract and reverse them, thereby preserving Heavenly Harmony (natural vital energy) and avoiding errors. Crude practitioners, however, act confusedly: reversing when they should follow, and following when they should reverse, much like someone going into the wilderness who cannot distinguish east from west. This is the third difficulty.

Diseases present with cold or heat patterns. Heat patterns require cooling agents, and cold patterns require warming agents; this is a constant principle. However, when the pattern of cold or heat is intense, abruptly attempting to reverse it may lead to rejection (gridlock) where the medicine fails to take effect. Using "treating heat with heat" (using hot herbs for true cold/false heat syndromes) and "treating cold with cold" (using cold herbs for true heat/false cold syndromes), although the initial nature of the drug matches the symptom, the ultimate outcome differs, allowing success. Crude practitioners fail to observe these nuances and treat indiscriminately. This is the fourth difficulty.

Medicinal properties involve Yin and Yang but are not limited to simple dichotomies; there are concepts such as "Yin within Yang" and "Yang within Yin." A difference of a hair's breadth leads to an error of a thousand miles. Crude practitioners fail to assess gravity and severity, administering drugs recklessly. This is the fifth difficulty. (From *Collected Works of Song Xueshi*)