有机体不仅学会做什么，还学会什么导致什么。

Sometimes we get sad about things and we don’t like to tell other people that we are sad about them.

Humans are predictably irrational in systematic ways.

It's sort of sad when you think of a kid like that going through life without a sense of humor...

解释：大部分药材都以新鲜为好，但艾草却以陈年的为佳，体现了药材使用的特殊性。