Economics: Marginal Thinking

The most important word in economics is marginal. Not average. Not total. Not what we have spent. The relevant question is always: what happens at the next unit? Should we hire one more engineer? Produce one more batch? Add one more feature? Run one more campaign? The answer depends on the marginal cost (what that next unit costs) compared to the marginal benefit (what that next unit produces). When marginal benefit exceeds marginal cost, do more. When it doesn't, stop.

This sounds obvious. In practice, organisations almost universally fail to apply it. They use average cost when they should use marginal cost. They treat past expenditure as a reason to continue when it is economically irrelevant. They ask "should we have done this?" instead of "should we do more?" Alfred Marshall embedded marginal analysis at the heart of neoclassical economics precisely because pre-marginal thinking — evaluating the total or average rather than the increment — systematically produces wrong decisions.

The sunk cost fallacy is the most costly failure of marginal thinking. Resources already spent cannot be recovered — they are irreversible. They therefore cannot and should not influence forward decisions. Yet Kahneman's research confirms that people weight sunk costs heavily: the pain of a loss already incurred motivates continued investment in failing projects far more than forward-looking analysis would justify. This skill's core move is to strip sunk costs from the analysis and restate the decision in purely forward-looking marginal terms.

Your Process

Step 1: Identify the margin Clarify what the decision is actually about. Is it: (a) whether to do one more unit of something, (b) how many units to produce/do/hire, (c) whether to continue an existing project or commitment, (d) how to allocate resources across competing uses? The answer determines what "marginal" means in this context.