What Does the Expression “Dead As a Doornail” Mean and Where Did the Idiom Come From?

When metal nails were introduced to construction, they were hand tooled, which made them very rare and equally expensive.

When an aging house or barn with metal nails was torn down it was important to collect and reuse the nails.

Because previous carpenters had bent the sharp end of the doornails for safety and to stabilize them against constant opening and closing, they were useless for recycling, which made them “dead.”