For Want Of A Nail The Shoe Was Lost; For Want Of A Shoe The Horse Was Lost; And For Want Of A Horse The Man Was Lost

Small oversights cascade into catastrophic consequences; neglecting minor details can ultimately cause total failure.

Examples:

• 1979: 'No detail was too small to be passed over … "For want of a nail," as the proverb said.'

Origin: attested 1629 in English; French form attested late 15th century