What is the key difference between a metaphor and a simile?

A metaphor creates a direct comparison between two unrelated things by stating that one thing is another, thereby highlighting similarities between them in a more implicit manner. For instance, saying "Time is a thief" suggests that time can steal moments from our lives, indicating a relationship without using "like" or "as."

In contrast, a simile explicitly uses "like" or "as" to draw a comparison, as in "Her smile is like the sun." This clarity in expression distinguishes similes from metaphors. The aspect about restricting usage to poetry in other responses is inaccurate, as both figures of speech can be found across different genres of writing, including prose.

Thus, the essence of a metaphor lies in its ability to convey deeper connections by suggesting one entity embodies the properties of another, providing a more profound or nuanced understanding of the subject.