Why 'Wai'?

Ramiro and I started taking Thai language classes. Our class has a small group of four, our neighbors Scot and Frieda are also taking the lessons. We have so far have learned the basics hello, how are you?, numbers, days of the week, ect...
One of the important cultural customs is the 'wai'. The 'wai' is pictured below. The hight of the hands in the 'wai' is the inverse ratio to the age or social position of the participants. Hand placement can be at chest level, nose level, or top of the head. The 'wai' is always accompanied with a bow and don't forget to smile.