Life expectancy might well be only 80 years by mid-century – about where it is now in advanced countries – if medical progress is disappointing or is offset by new threats or hazards. If we make provisions for long lives that are cut short, we will have wasted huge amounts of precious economic resources.
寿命延长计划中的主要困难是我们不知道我们是否真的会长寿。如果医学进步让人失望，或者被新出现的威胁和危险所抵消，到本世纪中叶，生命期望值或许也只不过能达到80岁——现在发达国家已经达到这个水平。如果我们为更长的寿命做好准备，而它却中断了，我们就会浪费大量珍贵的经济资源。但是如果我们没有为更长的寿命做足准备，许多老年人就会陷入贫困。