The garage door seems like a very simple piece of equipment, and it sort of is in the fact that it only has one function: to go up or down. But it actually takes over 20 different parts to have the garage door work right.
When you press the button and you want the door to lift or lower this sends a signal to the garage door opener. The opener, being like the brain, of the operation will send a signal to the drive and the springs. The belt and drive, being like the muscle, will actually do the lifting of the door. Even though it is a fairly simple process in theory it requires a lot of parts to do this process smoothly and quickly.