Remember everyone is emotional and that people are all going through the ups and downs of life, so try to comfort or cheer up others who get angry or are in a bad mood.
Perhaps this is an exaggeration. But the core of the message is that people tend to have stronger feelings about something than they let on. People who regularly have outbursts of anger, depression or flamboyant enthusiasm are generally frowned upon in most cultures. This especially applies to men (for women trying to figure us out). The application of this rule is to not assume everything is fine just because someone isn’t having a nervous breakdown. We all have our individual problems, angst and upsets that are normally contained.