like nailing jelly to a tree

adj. Used to describe a task thought to be impossible, esp. one in which the
difficulty arises from poor specification or inherent slipperiness in the
problem domain. Trying to display the prettiest arrangement of nodes and
arcs that diagrams a given graph is like nailing jelly to a tree, because
nobody's sure what prettiest means algorithmically. Hacker use of this term
may recall mainstream slang originated early in the 20th century by
President Theodore Roosevelt. There is a legend that, weary of inconclusive
talks with Colombia over the right to dig a canal through its then-province
Panama, he remarked, Negotiating with those pirates is like trying to nail
currant jelly to the wall. Roosevelt's government subsequently encouraged
the anti-Colombian insurgency that created the nation of Panama.

