All impact phrases use imagery. Imagery helps your listeners understand and remember. When you want to explain an idea, draw a mental picture and then color it in. Your job as a speaker is to get people to imagine, think, and feel. Saying something longed for was as "welcome as a glass of cool water after eating a very hot pepper" conjures up taste, heat, relief, and refreshment in your listeners' minds. Speakers have many verbal tools to paint pictures with, and two of the best are metaphors and similes.
These two popular figures of speech are similar to each other, and most speakers don't find it necessary to distinguish between them. Certainly their purpose is the same: to create a striking, vivid picture with few words. Metaphors and similes transfer the image of one thing to another. "Man is still the most extraordinary computer of all," is the metaphor John F. Kennedy used to describe L. Gordon Cooper. These devices are fast and effective. Ralph Waldo Emerson's "Hitch your wagon to a star" conveys instant advice to the ambitious and to dreamers. A sports writer for the New York Times described Barry Bond as being as warm and fuzzy as a frozen pool ball.
When you do create a metaphor or simile, make sure it is appropriate to your audience and style. And do your best to make it original. A worn-out cliché—"dead as a doornail" or "white as a sheet"—is weak. We have heard it so often that it no longer has impact. Try "dead as a dissected frog" or "white as the tips of a French manicure." Original figures of speech are the ones that attract attention and make the image stick in your listeners' minds. One speaker trying to duck hostile questions at a news conference said, "I somehow feel there's a boomerang loose in the room." That's a good, original metaphor.
Try not to mix up your images. "Now that Jim is back in the saddle, everything will be smooth sailing" is a mixed metaphor that paints a confusing picture of cowboys on the high seas.
A metaphor is a more direct, less subtle version of a simile. "Power is poison" and "Room for improvement is the biggest room in the house," are short, sharp metaphors. A simile compares unlike things, usually with connecting words such as like, as, or is. "He keeps himself in the public eye like a cinder" is a perfect, ear-catching simile. Here's a vivid one: Truman Capote once said, "Venice is like eating an entire box of chocolate liqueurs in one go."
People use metaphors and similes in virtually every speaking situation. Charles de Gaulle used one to make a political statement: "Treaties are like roses and young girls. They last while they last." I once heard a woman address a group for the second time; she said, "My stories are like good wine and good women—they improve with age."
Another useful figure of speech that creates magnificent imagery is hyperbole, which is purposeful exaggeration. "He could sell refrigerators to Eskimos" is a classic example. When Dorothy Parker shared office space with Robert Benchley she said they had an office "so tiny that an inch smaller and it would have been adultery."