Why Did Your Boss Hire You?

Someone explained why employees are hired to work. Your boss hires you because: 1) they need you to do something they don't know how to do, 2) they need you to do something they don't have time to do, 3) they need you to do something they don't want to do.

I'd like to add to that list: 4) they need you to something for less money than they can do it themselves.