Metaphors such as "she ran like the wind" have many interpretations.  "She ran like the wind" is used in english to me she ran fast.  Could it not also mean that as she ran she scattered leaves around like the wind.  Or that she howled while running as the wind howls.  That she was not deterred by the obstacles in her path.  That she ran down two streets at once then merged back together. 

Now while some of those possibilities are rather unlikely interpretations, there are many that are completely plausible.  Particularly depending on your experiences with wind.  If the wind where you live is always a light breeze, using the expression as meaning 'she went fast' has no grounding in your experience.

So where do we get the notion of what the metaphor means.  Well usually from context in the surround situation and previous encounters with the phrase.  Expecting a person (or computer) to arrive at the same idea based off a metaphor they have never heard before, without any context;  is much the same as expecting them to understand a word they have never seen before without any context. 

So to wrap up this point, becuase metaphors are not 1:1 there are many interpretations for any such metaphor.  If there are many interpretations it is not unreasonable that a person prefer one explanation over another.  Therefor it is not required that a computer be able to comprehend all metaphors on it's first encounter.  And instead can learn to treat some phrases as megawords that take on their own meaning based on the phrase's repeated use.