I can't understand why he failed.是什么意思？

I can't understand why he failed.

我不明白他为什么失败了。

understand

vt.& vi. 懂，理解；vt. 了解，默认，听说，领会；

例句
Another accusation levelled at the Minister is that he does not understand ordinary people...
另一个矛头则直指部长不懂得体恤百姓。

why

adv. （用于问句）为什么，为何，（反问，表示不必）何必，（说明理由）为什么；int. 呵唷，哎呀，嗨；n. 理由，原因，说明，难解的问题；

例句
Most people have very little difficulty in seeing why a Van Gogh is a work of genius.
多数人不难理解为什么凡·高的作品是天才之作。

he

pron. 他，它，一个人；n. 雄性动物；

例句
Logic had prevailed and he had abandoned the idea.
最终理智占了上风，他打消了那个念头。

failed

adj. 失败了的，不成功的；v. 在…中失败( fail的过去式和过去分词 )，衰退，衰弱，破产；

例句
They recently failed to negotiate a mutually acceptable new contract.
他们最近未能谈成一个双方都满意的新合同。