The normal body temperature is 98.6 degrees Fahrenheit; if it goes up even one degree there will be a disease in progress. Only when it is within the appropriate level does it indicate a healthy body. In the same way, your blood pressure is normal when it is 120 over 80. If the blood pressure goes up to 150 over 90 it indicates an abnormal condition in the body, which may be indicative of an illness. Similarly, the heart beat should be around 75; if it increases an ailment will be in progress.
The same is also true for your senses. There is a range of light that is appropriate to healthy functioning of the eyes. If the light is too bright the eyes cannot see and will be harmed. This is true, as well, in the case of the ears; there is a proper range of sound. If the level of sound exceeds that range, such as may happen close to an airplane, a train or a loudspeaker, the hearing will become impaired. Like this, all the senses are limited to a normal range of operation.
We see that life functions a lot like a limited company in the business world. If you want to carry on unlimited business with this limited company then you will be subject to a great deal of distress. Therefore, you have to impose restrictions on your behavior, and spend your life acting always within certain prescribed limits. This can also be called discipline. Discipline is particularly necessary for the spiritual progress of an individual. Without discipline a person is likely to become nothing but an animal. But discipline, too, has to be exercised within limits. There is even a need to regulate your discipline if you are to enjoy life. You see that for everything there is a limit and a boundary. If you stay within these limits you will not be troubled by life.
The Gita has taught that desire and anger are the primary obstacles to liberation, so it is vitally important that they be curbed. You need to take proper notice of these two dreadful enemies of man and develop complete control over them. These enemies are not external to you; they are your inner enemies. If you are defeated by your inner enemies, how can you ever hope to conquer your external ones? Once you keep desire and anger under firm check you will be able to defeat your outer enemies quite easily. The Gita has shown that the way to conquer desire and anger is by saturating your life with renunciation, sacrifice and love.