原文 'AN APARTMENT OWNER WOULD PROVIDE AN EXTERNAL BENEFIT IF SHE INSTALLED A SMOKE DETECTOR. bUT SHE DOESNT CONSIDER HER NEIGHBOR'S MARGINAL BENEFIT WHEN SHE IS DECIDING WHETHER TO INSTALL A SMOKE DETECTOR. THERE IS UNDERPRODUCTION'

我不明白为什么 EXTERNAL BENEFIT 就会造成UDERPRODUCTION.

讲一下呗

因为，非购买者能够享受到某种产品带来的好处，那么，相对来说，他就会减少购买，需求曲线左移，最后产量减少。低估了。我理解就这样。