Water and fire magnify this. Shaded slopes carry disease risk. Section 7 (“其树如瓜芦叶如栀子花如白蔷薇实如栟榈蒂如丁香”) is the nearby evidence: Poor drainage, low light and high humidity favour waterlogging and fungal disease; “unfit to pick” has empirical basis. This treats the text as a testable judgment, not a slogan.
Half a cup is water.