In realized metaphor, the intended referent is a real or intelligibly determinate entity for which a borrowed expression is used. A courageous human exists; calling that person a lion heightens the attribute of courage.
The language treats the person as though included within the class of lions, but it does not change external reality. The audience recognizes the rhetorical claim and receives the intended quality more forcefully.
That rhetorical identification accounts for the force of metaphor beyond a simple substitution of labels.