못해

In a sentence

• 시간이 없어서 준비를 못해.

  I couldn't prepare because I didn't have time.

  Here, '못해' indicates inability to perform an action due to external circumstances.

• 정말 미안해, 이런 실수를 다시는 못해.

  I'm really sorry, I won't make such a mistake again.

  In this case, '못해' expresses a determination to avoid a specific action in the future.

• 어제 밤에 너무 피곤해서 숙제를 못했어.

  I was so tired last night that I couldn't do my homework.

  Here, '못했어' (past tense of '못해') depicts inability to complete an action caused by a personal condition.