Marginal Impact
Is supporting impactful projects always the best way to achieve impact? And how do you know how much impact you're generating?
The marginal impact of an investment of time or money is the additional impact that this specific investment created. The term is usually used to emphasize that when you make decisions, you should take into account only the impact that was actually generated by your choice, rather than counting the impact of already existing efforts. For example, joining a huge movement with lots of impact isn’t inherently better than joining a small movement, if your own impact isn’t greater as a part of that movement.
If you’re a toaster manufacturer considering whether to manufacture one more toaster to sell, for example, the question you need to ask yourself is not whether the toaster business is profitable over all - but rather how much profit you’ll make on this next toaster. It may be the case that selling toasters is a lucrative business overall, but the market is already flooded with your previously-sold products and you’ll fail to sell another one. In this case, your total returns from selling toasters might remain large even if you manufacture another one, but your marginal returns (income minus expenses of this next unit) will be negative - so manufacturing it in the first place is a bad idea; you’re losing money.
As a result, it’s unclear that additional donations to Wikimedia lead to improvement in the content provided by Wikipedia. This is an example where the total impact (or even total cost-effectiveness) is a pretty terrible proxy for the marginal impact of additional donations. The first few millions of dollars that Wikipedia receives are incredibly valuable and important, but those are already a done deal - you can only control the marginal impact of the 100 millionth dollar or above.