The following aspects may explain this question. 1. Resonance Effect: In natural phenomena, the unity of opposites between matters is the main body of any exists. For example, up and down; left and right; anterior and posterior. Channels are divided into Yin and Yang and distributed in the interior and exterior aspects of the Zang Fu organs. When the acupuncture point of one side of body is needled, the other corresponding point located on the opposite side will generate the being-needled sensation as well. Hence, for pain or diseases on both sides of body and interior organ diseases, it is fine to needle only one side of body and there is no need to needle both sides of body. To treat pain, in general, the opposite of the more painful side or the opposite same name channel of the affected channel is selected. For non-pain diseases, select male’s left side and female’s right side. For example, to treat knee pain of both sides, select the left Neiguan (PC6) and right Taichong (LV3) as a combination, or right PC6 and left LV3. This type of point selection can reduce the total number of points at least half. 2. Correspondence Balance: The right and left side of channels are not isolated, but mutually influence each other. They cross and connect as well for retaining the dynamic balance between the upper and lower and left and right sides. It is well known that it is not the same sides of upper and lower extremities are moving while walking, but the opposite upper and lower extremities are coordinating. The coordination is retained mainly through the Du meridian. The connecting vessel of the Du meridian breaks from the main channel at sacrum and coccyx (DU1) and travels upward to the nape and head. It then travels downward to the scapula to connect to the foot Tai Yang channel and also penetrate into the spinal column (backbone). The connecting vessel of the Du meridian is the control center to retain the communication between the left and right and up and down. Needling the opposite point of the affected site will help the body gain the balance back. For example, needling the lower body when the disease is in the upper body. Needling the right side of the body when the disease is in the left part of the body. It is not necessarily to needle both upper and lower or right and left sides.