The Worker-Work Environment (W-WE) relationship formed a system. This concept is very important in-order to understand Ergonomics.
First let us understand what is a system?
*A system can be defined as an aggregate of interactive components operating together to perform a function. The key words here is aggregate and interactive. Aggregate - loose association of a components that are not necessary homogenous, but nevertheless are brought together to serve a purpose. These components is interactive which means they have a mutual or reciprocal effect, one upon other. Interactive in the sense that they are working in mutual harmony to perform a function. (source: The Worker at Work by T. Morris Fraser)
The harmony of this relationship will keep the equilibrium of this system. This is the MAIN FUNCTION of ERGONOMICS.