Anger is active sadness; sadness is inactive anger. They are not two things. Watch your own behaviour. When do you find yourself sad? You find yourself sad only in situations where you cannot be angry. The boss in the office says something and you cannot be angry; it is uneconomical. You cannot be angry and you have to go on smiling - then you become sad. The energy has become inactive. You come home, and with your wife you find a small thing, anything irrelevant, and you become angry.
