Nourishment opens with a line that already holds something worth keeping and puts it down. Legge's translation gives the image of an efficacious tortoise set aside while its owner stares at another until his own lower jaw hangs slack, and it names the result as evil without qualification. The tortoise of the Zhou period was an instrument of divination and, in the commentary tradition, a creature held to sustain itself on air alone. Either reading carries the same weight: the subject begins with a genuine means of nourishment that belongs to him, and loses it by watching somebody else eat.
The hexagram takes its whole shape from the mouth. A solid stroke at the bottom, a solid stroke at the top, and four yielding strokes between them draw the outline of open jaws, which is why the Great Symbolism, reading mountain above thunder, draws from the figure a counsel that words be watched and that eating and drinking be kept temperate. This first line is the lower lip of that mouth, the base of the lower trigram Zhen, and a yang stroke correctly occupies the odd place. Weakness is therefore not the fault on offer here. Capacity is present and goes unused.
What the imagery condemns is the posture rather than the appetite. A slackened jaw is a body arranged for watching rather than for eating, and the tortoise is lost to no thief. Set first in a hexagram concerned throughout with who is fed and by whom, the line establishes the error the remaining five will answer in turn: looking outward for what is already held, and losing the holding in the look.