Confusing Simile and Metaphor

[Erthona]

Primarily it is preference as long as one is describing something simply. Metaphor is a much more powerful tool than simile, especially extended metaphor. Metaphor is more difficult to control and a lot easier to screw up than is simile, thus it requires more effort on the writers part about how to use it. The "as" form, which is not often used today, is closer to metaphor, or at least that is how I think of it. If I say,

She is as hot as the sun,

that is very close to equating the two in terms of their attributes, although it does not equate she and sun themselves as metaphor would.

She is the sun, burning with a radiance that surpasses the eyes of men to comprehend.

Metaphor is not exclusive. When you say something is something, then it inherits all of it's attributes. With simile we can be more selective about what we wish and do not wish to attribute.

The princess is like the sun, burning with a radiance that surpasses the eyes of men to comprehend.

So using the same wording there is still a distinction between having this attribute of the sun, and having all attributes of the sun. The disadvantage to metaphor is you not wish to attribute all of the sun's qualities to her. The advantage is, they are there for further use, should you wish to avail yourself of them. This is especially true in an extended metaphor.

Dale