many small things can have a big effect; a pile of feathers can sink a ship
A yojijukugo proverb meaning that even tiny, seemingly insignificant things can accumulate and cause a major outcome. The literal image is that a large enough pile of feathers can sink a ship. Used to warn against ignoring small matters.
The proverb 'sekū chinshū' means that even small things, when accumulated, can become a great force.
A more common Japanese proverb with a similar meaning: 'Even dust, when piled up, becomes a mountain.' 積羽沈舟 is a less common, more literary Chinese-derived expression.
A yojijukugo of Chinese origin, from the phrase '積羽沈舟' (jī yǔ chén zhōu), literally 'accumulated feathers sink a boat.' The exact historical derivation is uncertain, but it is a classical Chinese proverb.