Thinking in Systems
Stocks are the tangible elements of a system.
Flows are the mechanisms that fill or drain stocks. The balance between the flows of a system will determine the behavior and level of the stock.
All system representations are simplifications of the real world.
A dynamic equilibrium occurs when at least one in flow and at least one outflow if present, but the level of the stock doesn’t change.
People quickly realize that increasing the in flow will grow the stock. But they miss that decreasing the outflow, while maintaining the inflow, will also increase the stock.
A change in the flow dynamics could take a long time to tangibly effect the stock.
Stocks act as buffers in the system allowing temporary decoupling of the in flows and out flows.
Feedback occurs in the system when the level of the stock can effect one of it’s flows. This process allows the system to self regulate.
A balancing feedback loop keeps the stock within a range or tries to reach an equilibrium enforced by an external factor to the flow. An example of reaching an equilibrium is a cup of hot coffee cooling off as it sits in a cold room.
Self reinforcing loops occur when the amount of stock enhances the rate of flow. This leads to exponential growth or runaway collapse.
Besides trivial examples, almost every system has a form of a feedback loop.