Imagine you're a government minister in a developing country, with responsibility for improving the lives of the poorest 20 per cent of the population. Given a blank slate, it's not hard to make a list: get everybody a basic bank account; pay a small cash sum to the poorest households; enrol every poor child in primary school, using sticks or carrots to make sure the children show up; provide handouts of cash or food to those hit by natural disasters; provide free basic healthcare and vaccinations. Such a list is ambitious, but not because it's too expensive. The real constraint is that to implement any of these policies, you need to be able to identify your own citizens.
假設你是某個發展中國家的一名政府部長，肩負著提高最窮20%人口生活水平的重任。面對著一張白紙，你不難列出計劃清單：給每個人開設一個基本的銀行賬戶；向最貧窮的家庭發放一小筆錢；將所有的貧困家庭子女送進小學，恩威并施確保他們不曠課；為遭遇自然災害的人分發現金或食品；免費提供基本醫療和疫苗接種。這些目標要實施起來顯得任重道遠，但原因不是成本太高。真正的難題在于，要落實其中任何一項政策，首先你必須能夠識別公民的身份。