What is the meaning of 所以?

therefore; so; consequently

Used in the first part of a sentence to indicate a reason that will be explained in the second part of the sentence.

the means (literally, "what one uses") by which; how

the manner in which; how

the reason why; why

proper behaviour; manners

reason, grounds

chữ Hán form of sở dĩ (“the reason why ... (is)”)

Source: wiktionary.org