因此...

Place 因此 at the start of your second sentence or clause. You first state the cause, then drop 因此, followed by the result. It acts like a pivot point. For example: 'It rained, 因此 I stayed home.' It makes you sound organized and thoughtful.

You will see this everywhere in news reports and textbooks. It is perfect for business emails when explaining a decision. Use it when you want to sound slightly more polished than the basic 所以. It works great in written Chinese or structured speeches.

Don't use it in a super casual setting like shouting to a friend at a loud bar. In those cases, 所以 is much more natural. If you use 因此 while eating street food with buddies, you might sound like a professor giving a lecture. It can feel a bit 'stiff' for pillow talk or venting about a bad date.

Chinese culture values logical flow and the 'Cause-Effect' relationship. Historically, formal Chinese writing (Classical Chinese) used very concise connectors. 因此 is a modern evolution that maintains that sense of order. It shows you have a clear mind and respect the listener's logic.

所以 is the casual cousin you see every day. 于是 is used when one action follows another chronologically. If you want to be incredibly formal, you might use 因而. But for most situations where you want to sound smart but reachable, 因此 is the winner.