어서 떨어지다

fall off because of something

떨어지다 is coming off, dropping, or being separated, and -어서 says what caused it: somebody knocked them off, the module split in two out in space, the weight loss made it slip off. 떨어질 줄 모르다 is the opposite — stuck fast and refusing to come away. The lines here are mostly literal falling rather than the figurative senses this verb can carry.

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