The sea is the deep subconscious below the surface mind, the wide inner water where dormant contents move unseen, and the fish drawn up from it is a single submerged thought or faculty lifted into the light of awareness. To cast a hook is to send focused attention down into that depth and hook one living idea, the first that rises, and bring it up where it can be examined. What lives beneath the surface holds exactly what the situation requires.
The coin found in the fish's mouth is the hidden value locked inside that risen thought, the piece of worth already present in the deep and released the moment the mouth is opened. Opening the mouth is the drawing out of what the depth was carrying, so the very thing needed to answer the outer demand is supplied from within rather than sought outside.
Sea: the deep subconscious below the surface mind, the inner water where dormant contents move unseen.
Fish: a single submerged thought or faculty raised from the depth into the light of awareness.
Hook: the point of focused attention sent down to draw one living idea up out of the deep.
Piece of money: the hidden value locked inside the risen thought, the worth already present in the depth and released when it is opened.