Being so concerned with the details of a problem, you can't see its overall structure.  Getting mired in the details usually means you aren't considering the bigger perspective.
-- KyleBrown

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There's a variant of this where your "map" of the problem uses metaphors which prevent you seeing what the real problem is. A different metaphor can simplify the problem immensely or suggest alternate approaches.

TomGilb has one about cannons and cruise missiles. The cannon only works if the requirements are right (aim that cannon).  When the shot misses, you modify the initial conditions and fire again.  The cruise missile evaluates its position and target frequently and makes mid-course corrections.  

The cannon is like the WaterFall methodology.  The cruise missile is like ExtremeProgramming.

Being too close to one view of the world is one cause of SelfSealingBelief''''''s.

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There is no problem with focusing with details if you vision yourself going from a whole to a number and taking it all in reverse to see the complete whole once your done with the single detail.

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See TaoTeChing