[suǒ yǐ]
（表示因果關系） so; therefore; as a result
He was busy, therefore, he couldn't come.
他忙得很，所以沒有來。
Because he works very carefully, he has not produced a reject in the last six years.
因為他干活兒很仔細，所以連續6年不出廢品。
He is old so his vision is dim.
他年紀大了，所以眼睛有點兒花。
That's just the point, otherwise I wouldn't come here.
所以呀， 要不然我就不來這了。
I know him well because he was formerly my fellow worker.
我所以對他熟悉， 是因為我和他一起工作過。
forget oneself
忘其所以
Overwhelmed by his achievements, he lost his reason.
他的成就使他高興得忘乎所以。