MENTAL MODEL · M10078

Law of Diminishing Returns

BusinessHigh supportEconomics

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Version 1.0.0 · Updated 2026-07-30

CORE DEFINITION

When other conditions remain unchanged, continuously increasing a certain input factor will cause the marginal output to gradually decline—the more input, the less output per unit.

SCAFFOLDING EFFECT

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Identify the inflection point of marginal benefit. It is not true that more input is always better; you need to find the optimal point where marginal benefit equals marginal cost.

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The law of diminishing returns (diminishing marginal returns) states: when technology and other inputs are fixed, continuously adding a variable input will cause its marginal product to first rise and then fall, eventually declining or even becoming negative. The reason is that the optimal factor combination is disrupted—for example, too much labor crowded onto fixed capital interferes with each other. It describes a short-run phenomenon (at least one factor is fixed). The optimal input quantity is reached when marginal benefit equals marginal cost; going beyond that is not worth it.

MINIMUM ACTION

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Practice this model in one real situation:

First, fix other inputs and identify the variable input being added. Second, observe how marginal output changes with increased input and find the inflection point. Third, compare marginal benefit (output value) with marginal cost (input price). Fourth, stop adding at the point where they are equal, which is the optimal scale. Fifth, periodically reassess, as changes in technology or factor prices can shift the optimal point.

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Source support: Explicit

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en.wikipedia.orghttps://en.wikipedia.org/wiki/Diminishing_returnsZH · Explicit
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