What is it to you: a flower, a dusty road, a never-ending night? Or would anything short of an essay be too simplistic an answer? To forge captivating, brief similes is often trouble enough, but depending on what is being described and in how much detail, extended metaphors may be called for.
In general, metaphors need not be explicit, like in the last line of Fizgerald’s Great Gatsby:
So we beat on, boats against the current, borne back ceaselessly into the past.
Here life (or time) is a river—a common enough trope that it can be toyed with implicitly.
On the other hand, metaphors can be explicit, like in the following quote from (and title of) Pedro Calderón de la Barca’s play Life is a Dream (1635):
What is life? A madness. What is life? An illusion, a shadow, a story. And the greatest good is little enough: for all life is a dream, and dreams themselves are only dreams.
(Act II, line 1195, translated from the Spanish by Edward and Elizabeth Huberman)
Penning the poetic finale of a Great American Novel or dramatising a metaphor into a full-blown allegorical play isn’t teachable by example. Exploiting an extended metaphor is.
In particular, any good example offers a template which can be reused, like Adán’s Quote of about life that I’ll work through today. (Translation by Katherine Silver.)