Learn Korean: 못하다 VS 못 하다

One important thing to pay attention to in learning Korean are the spacing rules. Even Koreans themselves are vulnerable to this kind of mistake. For example, they write 한번 instead of 한 번 and they write 못해 instead of 못 해. Wait, these two are actually both right, but it is still advisable to know the difference no matter how subtle. 못하다 (without the space) is used to describe things we are bad at doing or we suck at doing. We can add 잘 to emphasize the fucking inability.

난 수학 못해.
I suck at math.

승민이가 노래 잘 못해.
Seungmin sucks at singing.

우리 오빠가 운동 잘 못해.
My brother is not good at sports.

못 하다 (with a space) on the other hand is used to describe actions we are not capable of doing due to some circumstances. I can sing. I have a good singing voice. But I can't sing now because of sore throat.

목이 아파서 노래 못 해.
I cannot sing. I have sore throat.

난 오늘 공부 못 해.
I cannot study now. (something came up)

This is only true to 하다 verbs. 하다 verbs are split up in their negative form. Other verbs like 먹다, 마시다, and 자다 are never attached to 못.