The devil is in the details
Idiom about hidden complications / From Wikipedia, the free encyclopedia
"The devil is in the details" is an idiom alluding to a catch or mysterious element hidden in the details;[1] it indicates that "something may seem simple, but in fact the details are complicated and likely to cause problems".[2] It comes from the earlier phrase "God is in the details", expressing the idea that whatever one does should be done thoroughly; that is, details are important.[1]