We usually know that Chinese medicine is decocted twice, called the first decoction and the second decoction, and then the two are mixed and taken, but we do not notice why this is needed. Some people are greedy to save time and want to replace the second decoction with the method of prolonging the decoction time, but this method is wrong. During the decoction process, the active ingredients are gradually dissolved in the soup from the inside of the herbs, but the drug is not always dissolved, when the internal and external concentrations reach a balance, it will stop dissolving or slow down the dissolution, which is necessary to filter out the juice and add water for the second decoction to establish a new concentration difference, so that the drug continues to dissolve. Some drugs are less soluble in water and harder to be dissolved, so they usually need two decoctions to be dissolved. If it is difficult to be dissolved by only one decoction, the active ingredients will still be less dissolved if the decoction time is increased in time, therefore, Chinese medicine cannot be decocted for a long time instead of two decoctions.