Usually we don't choose metaphors consciously and yet they're in the back of our minds guiding our interpretation of what's happening and our expectations of what will occur. Sometimes they support us and sometimes they don't. A metaphor is a comparison of one thing to another. My love is a red, red rose. Life's a bowl of cherries, say some.
Life's the pits, say others.
It's a jungle out there. A delicious smogasboard. Life's a game. The Myth of Sisyphus tells the story of an extended life metaphor. Sisyphus was condemned for eternity to push a giant rock up a mountain and watch it roll down.