You don't have to count all the leaves on the tree, you can take a sample and you count that and then you multiply.

你不必数树上所有的叶子,你可以抽样,然后计数,再相乘即可

耶鲁公开课 - 金融市场课程节选

This is very important,which is why I am doing it: "If we want to know how fast a human being can run, then it is no use to average out the speed of a "good sample" of the population; it is far better to collect Olympic gold medal winners and see how well they can do.

这话非常重要，是我作这个研究的原因：,“如果想知道人类最快能跑多快，那从好的样本中测出平均数是“,没用的;,而应该收集田径类奥运冠军的信息,看他们能跑多快。

哈佛公开课 - 幸福课课程节选