People systematically misjudge accumulations. They confuse a stock (a quantity that builds up: cash, debt, a customer base, a backlog, technical debt) with the flows that change it, and infer the stock's direction from a flow's direction. The classic error: "the inflow is falling, so the stock is falling." It is not - the stock keeps rising while inflow exceeds outflow. This skill makes the structure explicit: name the stock, name its inflows and outflows separately, and reason about its trajectory from the net flow. The output is a stock-flow map. It corrects a specific, well-evidenced accumulation error; it does not claim to teach systems thinking wholesale.
When to Use
- A quantity accumulates over time (runway, debt, backlog, headcount, customer base, reserves, technical debt) and the question is whether it is rising or falling.
- A trend in a flow is being used to infer the stock ("churn dropped, so the base is growing").
- Before acting on an "it's getting better/worse" intuition about an accumulation.
When NOT to Use
- The quantity does not accumulate (a one-off event, a ratio with no stock).
- A simple direct relationship with no accumulation is all that is at play.
- Mapping forward consequences (use futures-wheel) or systemic causes (use iceberg-model); this is specifically about accumulation dynamics.
Instructions
When asked to reason about an accumulating quantity, follow these steps:
- Name the stock. The quantity that accumulates, and its current level if known. Make sure it is a stock (a level), not a flow (a rate).
- List the inflows. What adds to the stock, and at what rate / trend.
- List the outflows. What drains the stock, and at what rate / trend. Do not skip the outflow - ignoring it is a common error.
- Compute the net flow. Inflow minus outflow: is the stock currently gaining or losing, and is the net flow itself trending up or down?
- State the corrected trajectory. What the stock actually does (rises / falls / plateaus and when), derived from the net flow, not from any single flow's direction.
- Name the naive intuition it corrects. What someone would wrongly conclude from the flow alone, and why it is wrong.
- Emit the stock-flow map per
references/TEMPLATE.md.
Output Format
Use the template in references/TEMPLATE.md. The deliverable is the stock-flow map with the corrected trajectory, not prose.
Quality Checklist
Before finalizing, verify:
- The stock is genuinely a level (accumulation), not a flow/rate.
- Both inflows and outflows are listed; the outflow is not ignored.
- The trajectory is derived from the net flow, not from one flow's direction.
- The naive intuition being corrected is named.
- No overclaim: it corrects an accumulation error, it does not teach systems thinking wholesale (see
evidence/dossier.md). - The output is the stock-flow map artifact, not prose.
Evidence
Tier S. The underlying failure is robustly demonstrated: across repeated experiments, including with highly educated subjects, people misread stock/flow relationships and infer stock direction from flow direction (Sterman's accumulation experiments; Cronin, Gonzalez & Sterman 2009; Meadows, Thinking in Systems). The strong evidence is that the error is real and that making the structure explicit removes it on a given problem; it is not a claim of broad systems-thinking transfer. Evidence is from human reasoners, transferred to AI use, not AI-validated. Full grading: evidence/dossier.md.
Examples
See references/EXAMPLE.md for a completed stock-flow map.