약하다
ya-ka-da
Why 'can't hold your drink' is the same picture as a low flame
The picture The force is thin, so the slightest press pushes it back or snuffs it out. 약하다 is being pushed back by the slightest press; 세다 is force loaded up enough to push.
Where the picture shows up in 약하다
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a flame with thin force
불을 약하게 줄여 주세요.
bu-reul ya-ka-ge ju-ryeo ju-se-yo
Please turn the flame down low.
The gas flame sits low and barely warms the bottom of the pot
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a body with thin force
아이가 몸이 약해서 자주 아파요.
a-i-ga mo-mi ya-kae-seo ja-ju a-pa-yo
The child is frail, so he gets ill often.
One cold draught passes and the child is straight back in bed
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a signal with thin force
여기는 전화 신호가 약합니다.
yeo-gi-neun jeon-hwa sin-ho-ga ya-kam-ni-da
The phone signal is weak here.
The waves from far away leave barely one bar, and the speech cuts in and out
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a body pushed back by drink
저는 술에 약해요.
jeo-neun su-re ya-kae-yo
I can't hold my drink.
One glass is enough for your face to go red and your body to tip backwards
'~에 약하다' pictures you being pushed back by that thing.
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a heart that folds when pressed
마음이 약한 사람은 거절을 못 해요.
ma-eu-mi ya-kan sa-ra-meun geo-jeo-reul mot hae-yo
Soft-hearted people can't say no.
The 'no' that was on its way out gets pressed by one request and simply folds
All of it in one picture
약하다 is one picture: the force is thin. Thin in a flame and it barely warms the pot; thin in a body and one cold draught puts you to bed. Thin in a signal and speech cuts out; and if one glass already tips you back, you are 술에 약하다. Thin in the heart, and your 'no' gets pushed back by a single request.