Flows change the levels of stocks over time
Flows (inflows or outflows) change the levels of a stock over time. The aggregate history of all flows within a system results in the current stock.
Stocks change over time through the actions of a flow. Flows are filling and draining, births and deaths, purchases and sales, growth and decay, deposits and withdrawals, successes and failures. A stock, then, is the present memory of the history of changing flows within the system.[1]
Stocks are more apparent than flows, especially outflows.
The human mind seems to focus more easily on stocks than on flows. On top of that, when we do focus on flows, we tend to focus on inflows more easily than on outflows. Therefore, we sometimes miss seeing that we can fill a bathtub not only by increasing the inflow rate, but also by decreasing the outflow rate.[2]
See also:
- Stocks are the quantifiable stores of a system
- Systems Thinking perceives the relationships and structure of complex systems
Thinking in Systems – Meadows (2008), § “Part One: System Structure and Behavior” / “One: The Basics.” ↩︎
Ibid. ↩︎