Metaphor is a comparison between two dissimilar things without using the word "like" or "as" to make the comparison. It's been said that the greater the difference between the two things being compared, the better the metaphor, and this is a notion with which I agree. For example, when asks to create a metaphor, a student of mine once wrote, " Football is baseball." Though this is arguably a metaphor, it generally would not be regarded as a very good one because the object of comparison are too similar."Football is chess" Would be an improvement, because the object of comparison are more dissimilar.