And don't be surprised if your taxi driver suddenly lets go of the steering wheel to perform a wai and thereby show his respect for a sacred place or object. If the object of respect is a Buddha image you should repeat the whole process three times. The position of the wai shows that you don't hold any weapons and that you come in peace. The Western handshake is believed to have the very same origin since it has evolved from the touching of the empty sword hands. But the wai is far more than the handshake is.
Handshakes are between equals, a wai is performed to admit inferiority.
The inferior always initiates the wai. Historically, the weaker man would be the first to show that his hands contain no weapons. The lowered eyes and head also takes away the ability to defend oneself. The superior may or may no return the wai. If you wai a monk or someone from the royal family they will certainly not return it.