[suǒ yǐ]
（表示因果关系） so; therefore; as a result
He was busy, therefore, he couldn't come.
他忙得很，所以没有来。
Because he works very carefully, he has not produced a reject in the last six years.
因为他干活儿很仔细，所以连续6年不出废品。
He is old so his vision is dim.
他年纪大了，所以眼睛有点儿花。
That's just the point, otherwise I wouldn't come here.
所以呀， 要不然我就不来这了。
I know him well because he was formerly my fellow worker.
我所以对他熟悉， 是因为我和他一起工作过。
forget oneself
忘其所以
Overwhelmed by his achievements, he lost his reason.
他的成就使他高兴得忘乎所以。