Well, there’s a venerable English proverb that warns, “The Devil is in the detail.”
The idiom "the devil is in the detail" refers to a catch or mysterious element hidden in the details, and derives from the earlier phrase "God is in the detail" expressing the idea that whatever one does should be done thoroughly; i.e. details are important.
And, the wiseGEEK, has this to say:
The slang term “the devil is in the detail” has a number of different senses. All of the meanings for the term boil down to the fact that it is often the small details of something which make it difficult or challenging. These details can prolong a task, or foil an otherwise straightforward dealing. Like many proverbs which involve the devil, it is meant to sound a note of caution. It may also be used to excuse or explain the obfuscation of an otherwise very simple project or task.
Often this expression is used when a project has fallen short of what one would expect (such as a poem whose themes and rhyme schemes are tight but whose rhythm is still off meter) or as a reminder that paying attention to critical details enables the final product to achieve a desired level of "quality".