면 썩다

if X, it rots

썩다 is rotting — food left out, fallen leaves, a sewer smell. -(으)면 supplies the condition, usually neglect or time: 그대로 두면 썩는 거야 'leave it as it is and it rots', 500년이면 썩어 없어진다는데. It carries a moral use as well, for anything that stagnates when cut off: 고립되면 썩어, said of water and meant about more than water.