For example, the pursuit of universal primary education in Sub-Saharan Africa would yield a lower, but still significant, $7 of social and economic benefit for every dollar spent. And efforts to achieve universal primary education worldwide would cost far more, with each dollar spent bringing just $4 worth of benefits.
目标雄心越大，影响会越小。比如，追求在撒哈拉以南非洲完全普及小学教育会降低每一美元投入的社会和经济收益，但仍有7美元。实现全球普及小学教育的成本要高得多，每一美元投入只能产生4美元收益。