Words are tools. Choose the right ones in the right sequence and you may seem smarter than you really are, but be sloppy in choice of words and people may think you are a sloppy thinker. Metaphors were supposed to be clever ways of expressing yourself. Of course they can be that, but they are also much more.
Recently finished reading "I is an Other" by James Geary in my quest to understand how to use words better or at least fathom the process. The title phrase comes from an aspiring young poet, Arthur Rimbaud who went onto a wide variety of accomplishments. such as a financier, arms dealer, explorer, anarchist. It is supposed to embody the key to a metaphor.
Definition: A metaphor is a figure of speech which makes an implicit, implied or hidden comparison between two things that are unrelated, but share some common characteristics. They are used often unconsciously to make sense of something new or confusing.
Metaphors are basically combining a target with a source. Comparisons to make the meaning more clear, although sometimes the connection is difficult. A modern example is "email"--taking something without a name and comparing it to something we are familiar with. An older one comes from Robert Hook after using primitive microscopes studying plants was the first to note the small pieces which reminded him of monk's cells and they became known as cells for no other reason. C.S. Lewis points out the unknown can only be made known through metaphor and analogy.
Metaphors are human inventions that help us figure things out, i.e. advance civilization. It is not restricted to any one language, but rather is universal. Giambattista Vico from the 1700s in Naples noted that different languages described inanimate objects with human attributes such as lip of a pitcher, neck of a bottle, mouth of a river. The effectiveness of a metaphor is not on the truth of the association, but on their easy accessibility
A metaphor can be like a joke with an unexpected twist and violated expectations
An identifier of an autistic person is they take words literally so often metaphors are frustrating for them.
In the U.S., football is often used metaphorically even by non fans. Fumble an opportunity, kick-off, huddle, throw a Hail Mary.
An effective metaphor was used by Obama, "if countries like Iran are willing to unclench their fists they will find an extended hand from us."
Judith Williamson pointed out that ads create objective correlations for mass consumption linking product to status, sex, wealth, intimacy and security. Image trumps information.
Metaphors can be poor if the comparison is not apt--accused of being misleading (such as by sales people). Or if they are too novel they can pass over the head of the recipient.
The author changes a common translation of the most famous philosophical statement--"Cogito ergo sum" from "I think therefore I am" to "I shake things up therefore I am." Cogito originally meant to shake things up and can be considered a metaphor.
Read the book to get a fuller feel for metaphors or if you are a bit impatient try this 9 minute video of James Geary where he uses the great philosopher, Elvis Presley to make a few points. https://www.ted.com/talks/james_geary_metaphorically_speaking?language=en