A system is a set of interrelated and interdependent parts arranged in a manner that produces a unified whole.
The two basic types of system are closed and open. Closed systems are not influenced by their environment and do not interact with it. By contrast, an open system recognizes the dynamic interaction of the system with its environment. Today, when we call organizations "systems", we mean open systems; that is, we accept that an organization continually interacts with its environment.
The health system is very much an “open system”. This is important to understand this as an advocate. When wanting to influence decision makers, you need to understand that they operate within an “open system” and they are influenced by many factors and players. Your case is not the only case. You should be aware of the competing influences on the decision-makers you want to influence. The job of the advocate is to ensure that everything influencing the decision-makers is understood and considered when developing a plan of action to influence them in the making of policy.