Comprehensive history and physical examination is a prerequisite for proper diagnosis. Even in large hospitals, no matter how advanced the instruments are, they can only be an extension of the human senses and cannot replace history taking and physical examination. On the contrary, only on the basis of careful and comprehensive questioning of the patient and formal and rigorous examination of the physical signs can these instruments be applied in a targeted manner. For example, a middle-aged man with low fever, cough and weakness for more than a month, with no abnormal findings on physical examination, was successively treated as “upper sensation”, “tuberculosis” and “typhoid fever” and failed, so he was transferred to a large hospital in Shanghai. He was referred to a major hospital in Shanghai for various examinations and consultations, and a lung tissue biopsy was taken before he was diagnosed with “pulmonary connective tissue disease”. However, three months later, hemiplegia and aphasia appeared again, and by chance, his family found that the sputum coughed up on the floor was different and asked for sputum examination, and the diagnosis of pulmonary schistosomiasis was confirmed. After asking for medical history, the patient was found to have eaten several drunken crabs before the onset of the disease. Another 16-year-old female was admitted to the hospital with “cause of convulsions to be investigated” because of leg pain for more than a month and convulsions for 4 hours. The blood pressure of the left upper extremity was 160/110 mmHg, which was not consistent with her age, while the right side was not measured, and the right carotid and femoral arteries were weakened. The next day, the director also agreed and later confirmed by angiography. A middle-aged male was diagnosed as “liver metastasis of gallbladder cancer” by MRI in a foreign country due to epigastric pain, vomiting, fever, and emaciation, and came to Beijing with a ray of hope. The abdominal ultrasound later showed two stones located at the base and neck of the gallbladder, and the wall of the gallbladder was 1.3 cm thick as confirmed by surgery. Special attention was paid to what was seen. The correct diagnosis is one that reveals the essence of the disease and conforms to the objective reality. Although various diseases have their common patterns, their manifestations can be very different in specific patients due to genetics, environment, living habits, individual reactions and other factors. Doctors should be good at extracting the essence of the coarse, remove the false and keep the true, from this to the other, from the surface to the inside. Those special examinations, such as CT, MRI, for cerebrovascular disease and tumor, and ultrasound for cardiovascular disease, are of great importance; and those special symptoms and signs often reflect the essence or suggest important clues for diagnosis, so special attention should be paid to them. A young woman came to the hospital in an emergency with headache and vomiting for 6 hours, and her lumbar puncture showed bloody cerebrospinal fluid. However, the doctor found that there was blood in the nasal cavity and right ear canal, which was apparently difficult to explain by “subarachnoid hemorrhage” and was presumed to be caused by skull base fracture, and saw that the patient answered the question in an obscure way. Zhang was admitted to the hospital with epigastric pain for 4 hours, and the diagnosis of “Marfan’s syndrome” was made on examination because of a double murmur in the aortic valve area and long fingers, which was later confirmed by ultrasonography. A male, 9 years old, was admitted to the hospital with “acute cellulitis” because he had fever for 3 days and developed urticaria with palpitations and right knee pain after intramuscular injection of Anacin, which was suspected to be acute rheumatic fever, and later developed swelling and pain in the right calf. The patient was discharged a year later with the diagnosis of “Staphylococcus aureus sepsis, acute osteomyelitis, acute cellulitis, and chronic osteomyelitis.” The analysis of difficult cases is often a comprehensive analysis of all clinical data, summarize the characteristics of the case, and then grasp a major contradiction or a group of symptoms, associate several possibilities, apply the exclusion method to gradually narrow the scope, speculate on the location and nature of the lesion, put forward a preliminary diagnosis, and use it to explain the clinical manifestations, such as the more reasonable explanation, the more adequate, the greater the possibility of correct diagnosis, such as can not explain If the main clinical manifestations cannot be explained, the possibility of having two or more diseases or complications at the same time or even other diseases should be considered. A man, 56 years old, was found to have fallen to the ground and sent to the emergency room with an electrocardiogram showing III°A-VB. However, the patient often wanted to sit up and was irritable, which was difficult to explain by simple arrhythmia. Another example is a male who was admitted to the hospital with sudden aphasia followed by dysarthria and left-sided hemiparesis for 1 year. This case was characterized by “hypertension, cerebrovascular embolism, and hepatosplenomegaly”, which is a common cause of cerebrovascular accidents and hepatosplenomegaly, but only true erythrocytosis and myelofibrosis were found to be present at the same time. The diagnosis was true erythrocytosis, and a consultation with a professor from Beihang Medical University was requested and the above diagnosis was agreed. A female, 26 years old, was admitted to the Department of Urology for the fourth time due to urinary retention, and no abnormalities were found in the cerebrospinal fluid and spinal cord MRI. The diagnosis of “optic neuromyelitis optica” was made after the diagnosis of “optic neuromyelitis optica,” as the patient had a transient visual impairment six months ago. Learning to update and improve the level of medical treatment is, in a sense, guided by philosophical ideas, based on the respective characteristics of the disease, the use of drugs or equipment to relieve the patient’s suffering. For medical workers, dealing with patients’ lives, learning the business is extraordinarily important. Low level of practice, insufficient knowledge, improper diagnosis and treatment, not only affect the effectiveness of treatment, and even endanger the lives of patients. In addition, science is developing, knowledge is updating, must continue to improve business skills. I know that the conscientiousness of learning, sustained energy from the spirit of enterprise and career, from the high standards, strict requirements, so as to be proactive, persistent, never complacent, and strive for excellence. In 1992, I went to the hospital in Inner Mongolia to assist in the work. He saw an 8-year-old girl with anemia and splenomegaly for 3 years and was unable to be diagnosed in the provincial capital, Jilin and Changchun. On examination, the spleen was 2 cm below the umbilicus and the erythrocytes were increased, so the diagnosis of hereditary spherocytosis was made by looking up the data and reading the blood smear against the chart. A 25-year-old female was admitted to the hospital with abdominal pain, cessation of defecation and exhaustion for 5 days. She had a history of 3 previous intestinal obstructions and was treated surgically on one occasion. On this occasion, she improved with symptomatic treatment, but was referred to the department for treatment because of episodic convulsions. Later, he gradually developed hypertension, paroxysmal tachycardia, fever, low blood sodium, tetraplegia, mute voice, dysarthria, difficulty in urination, EEG showing extensive slow waves, and increased cerebrospinal fluid protein. Convulsions are commonly seen in grand mal seizures, but can be excluded from the seizure form and EEG. In vegetative seizures, clinical tachycardia, elevated blood pressure, chills, fever, a few with impaired consciousness, and twitching of the extremities are common, but abdominal pain and paralysis are difficult to explain and do not support abdominal epilepsy. Upper and lower motor neuron lesions can cause paresis, but this case is easily excluded. Myasthenia gravis and periodic paralysis may also be excluded. Hematoporphyria is a rare metabolic disease of unknown origin. Acute intermittent hepatic hematoporphyria is most commonly seen in women aged 20-40 years, with three major clinical manifestations: cutaneous, abdominal, and neurological syndromes. Hyponatremia may be present with damage to the inferior optic thalamus, hoarseness and dysphagia with damage to the cranial nerves, hypertension with vegetative disorders, and occasionally sphincter disorders. In this case, the urine was red after heating, and the diagnosis was confirmed by positive urine porphobilinogen and hematoporphyrin by Concord Hospital. In conclusion, the correct diagnosis depends on the doctor’s knowledge, clinical data, thinking style and clinical experience. However, as Zhang Xiaoqian’s mentor said, “In fact it is unlikely to achieve a completely correct diagnosis; each diagnosis, no matter how deepened, is only an understanding of a certain stage under certain conditions.” By facing this point squarely, clinicians can be humble and cautious, work hard and keep moving forward.