To determine a simile's purpose, separate three stages. First identify its structure: subject, comparator and shared respect. Second ask what the listener already knows. Third ask what new understanding or response the speaker intends to produce.
Example 1: an exceptional person can arise among ordinary people, as musk arises from gazelle blood — possibility.
Example 2: a cloth is as deeply black as a raven — degree.
Example 3: known fruitless labour resembles writing on water — reinforcement.
Example 4: a hungry person likens a bright face to a loaf — preoccupation.
The marker used, the image's attractiveness, or a surface reading of the words does not by itself settle the issue; the situation of utterance remains decisive.