모르겠다

In a sentence

• 저는 여기에 왜 왔는지 모르겠어요.

  I do not know why I came here.

  The word '모르겠어요' is used to express uncertainty or lack of knowledge about the reason.

• 그는 언제 올지 모르겠어요.

  I do not know when he will come.

  '모르겠어요' here signifies uncertainty about a future event.

• 이 문제는 너무 어려워서 모르겠어요.

  This problem is too difficult, so I do not understand it.

  '모르겠어요' expresses lack of comprehension due to difficulty.