所以然

kàn bù chū lai gè suǒ yǐ rán

看不出来个所以然

not be able to see the whys and wherefores

tā jiǎng le jǐ gè xiǎo shí dàn duì zhǔ tí yě méi shuō chū gè suǒ yǐ rán lái

他讲了几个小时，但对主题也没说出个所以然来。

He burbled on for hours but made you none the wiser about the topic.

zhī qí rán què bù zhī qí suǒ yǐ rán

知其然却不知其所以然

know that something is so but not why it is so

shǎ hū hū de wǒ jiù zhè yàng shǎ hū hū de yǐ zhe chuāng hu bǎ nà jù huà sī suǒ le dà bàn tiān zuì hòu hái shi méi yǒu xiǎng chū ge suǒ yǐ rán lái

傻乎乎的我就这样傻乎乎的倚着窗户把那句话思索了大半天，最后还是没有想出个所以然来。

Silly silly so I leaned against the windows, put the words to think of most of the day, but finally did not come up with it herself!