"God is in the detail(s)." Concisely expressing the idea that details matter, and whatever it is you're doing should be done thoroughly & with an attention to detail. This is a proverb, an idiom & a quote, that has been quoted, and re-quoted plenty of times, and has been attributed to many people over the years.
It is most commonly attributed to Ludwig Mies van der Rohe, and while it probably didn't originate him, it was even referred to in is 1969 New York Times obituary.
This particular saying was also a favorite of Aby Warburg (a German art historian), though it probably didn't originate with Warburg either.
"The good God is in the detail." a variation on "God is in the detail." is usually attributed to Gustave Flaubert.
In Bartlett's Familiar Quotations, the author of "God is in the detail" is listed as anonymous.
The popularity of this quote has led to a number of variations on it. Most often said as "God is in the details." it can also be said singularly, "God is in the detail." And it's most common variant "The devil is in the details." can also be said as "A devil is in the detail." (or "details).
Ironic that the history & origin of a quote reminding us to pay attention to the details is vague on a range of specific details, but whether the phrase originated with Ludwig Mies van der Rohe, Aby Warburg, Gustave Flaubert, or someone else entirely, the point still remains - more often than not, when something goes screwy it's because we forgot to pay attention to the detail(s).