이건

이건

"This" or "this thing."

In this sentence, '이건' emphasizes 'this', referring specifically to the discovery being mentioned.

이건 정말 대단한 발견이다.

This is truly an amazing discovery.

Here, '이건' is used to point out the subject, the topic of the difficulty being discussed.

이건 너무 어려워서 이해할 수 없어.

This is too difficult to understand.

In this example, '이건' indicates 'this' and connects it to a previously mentioned statement or context.

이건 내가 아까 말했던 거야.

This is what I told you earlier.