Yawning is contagious, we all know that (different theories such as the brain-cooling theory exist). Same with smiling. Unfortunately, so is obesity. Two people living together start looking like each other, mostly due to shared diets and eating habits and simple imitation of facial expressions. Couples who end up looking alike also tend to be happier.
Knowing that smiling is contagious, put visual clues in places where you need it. Stick a smiley on the mirror to see first thing in the morning, on your desktop, at the end of your presentations, or on your way out the door. It actually works.
“You are the average of the five people you spend the most time with.”