This is the 6334th most frequent Korean word.
아니어서
"아니어서" means "because (it is) not" or "since (it is) not."
This uses "아니어서" to explain the machine's non-functionality as the reason for the inability to complete the work.
기계가 작동하지 않아서 우리가 작업을 못 했어요.
The machine wasn't working, so we couldn't do the work.
In this sentence, "아니어서" is used to express the reason for being surprised, forming a cause-and-effect relationship with the preceding clause meaning "not true."
그것은 사실이 아니어서 놀랐어요.
It wasn't true, so I was surprised.
Here, "아니어서" indicates that the lack of rain facilitated the action of going outside, showing a contrasting situation.