What is the difference between 竟然 and 居然? As I know, 竟然 and 居然 both mean "unexpectedly". Do they have any difference?
They are very similar. The difference is that 竟然 is more used in a negative situation where the unpleasant result is out of control and beyond the expectation, while 居然 could be used in both good(i.e. surprise) and bad (i.e. accident).