Every single day, I keep in mind his words and try to be in a good humor. It's sometimes hard, but we should be that way because people's mood is contagious.
Alain explains in his book how a person's bad mood affects his surroundings.
If you were in a bad mood and gave a look of hostility to a waiter or a person who is sitting next to you in a restaurant, that would be a beginning of disaster. A frown on your face passes from face to face and everybody near you starts to have troubles. Glasses will be broken. The waiter will beat his wife that night. You should remember how a bad mood is tending to spread from person to person.