Express anger and chances are you will bring down the mood of all those who witness it. Express joy, and you will do the opposite. Humans, like all animals constantly watch and react to the actions of those around us. It’s why it is so very important to surround yourself (as much as possible) with others who reflect the values and outlook you wish to have. So, if you need more optimism in your life, begin developing yours by paying attention to who in your community spreads joy and concern for others rather those who constantly complain and criticize.