Like putting the horse before the cart
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At some point in our lives we are shocked and amazed by the quality amusements that television such as the Discovery channel offers, something along the lines of:

"Locusts are nothing more than your common garden variety grasshopper gone awry. When the back legs of a grasshopper are tickled, they become agitated and begin to change colour, eventually becoming so overwhelmed by pure rage that they tear around with the sole aim of forming a swarm and devouring everything in their sight. Their erratic movement often causes other grasshoppers to be tickled likewise, giving rise to unimaginably huge numbers of deviant grasshoppers, better known as locusts."

or

"When the common starfish (Asterias rubens) is threatened, it often expunges its internal organs in a bloody (as bloody as starfish can get, surely) stream to stun and distract its attacker. It then moves away and regenerates a new set of organs."

Well and good, absolutely fascinating stories that only scratch the surface of nature's complexity. I would have just left them as that, marvelling at them for a while before relegating them to the margins of my memory like those tissues deep in your pockets that you forget about and disintegrate in the wash and leave a carpet of tiny white fluff on your best pants before an important dinner. But sometimes, when faced with such tasty nuggets of hardly any consequence, people like to turn them into metaphors for other, supposedly more important and weighty matters. It's not difficult to do this:

"The good side of mankind, like the grasshopper, is separated from immutable evil by the thinnest of lines, tipping into this dark pool at only the very suggestion of a stimulus. Evil, being universal and all-pervasive, then quickly subverts other forces of good, "etc., blah and so on about good inevitably being the victor (how many people have seriously seen a real, buzzing, snarling locust? What about a charming green grasshopper?) and about the starfish representing people who would rather sacrifice their inner morals than their image/material comforts in the face of danger and adversity.

But that's like putting the cart before the horse, the peanut butter before the bread. Metaphors were invented to explain a particularly knotty circumstance or concept by translating them into easier to understand terms, without losing much of the meaning (though this seems a tall order if the most common metaphors are things like buying fruit at the market or washing a plate) and not vice versa. Often, it's because people think that a certain phenomenon or situation of a certain exquisite but wholly restricted perfection is just itching to be a metaphor for something. Something like seeing a nice cue ball and buying a pool table to match (this is probably the source of some of the worst metaphors ever, a crime that I am terminally guilty of).

In some respects this is better, fitting aspects of real life to some hypothetical but entirely probable situation like a canvas where the palette of infinite possibilities provided by human nature can play upon rather than imagining some contrivance of real life that would adequately describe some scene of the climax of human pathos. It does lend itself much utility in finding for us increasingly apt means of representing things that we encounter every day. In a more or less certain search for meaning of varying degrees, it is one of our more powerful tools.

(Like a sledgehammer, rather hit-and-miss.)