Having worked in a variety of customer service jobs I know how hard it can be to be cheery when there is a continuous flow of disgruntled and just plain grumpy and crotchety folks. It doesn't matter how rude a customer was, I had to be kind. Or what type of nastiness a customer unleashed on me the day or week before I had to be kind the next time I saw them.
But what I know is that being in a position that requires you to be cheery and smile (no matter what) does something to you.
For one, smiling and being friendly all day makes it really hard to be upset about the small things. Being friendly to others helps them be friendly to you. And if you have a tremendous amount of friendly interactions in a day, every day, every week...well then things appear to be rosier and you are in turn a more cheerful person. Not to mention your upbeat attitude most likely brightened someone else's day.
Imagine what our students' lives would be like if we set and expected this model in our classrooms? lmagine what the world would be like if everyone behaved like this everyday? Try it and see.