估计问题的性质不同。在这里，我们不关心检验特定的假设，而是关心估计参数的值。

The way in which men produce their means of subsistence depends first of all on the nature of the actual means they find in existence and have to reproduce.

Ideas are like fish. If you want to catch little fish, you can stay in the shallow water. But if you want to catch the big fish, you've got to go deeper.