Why or How did the term Dead as a Doornail originate?

The phrase "dead as a doornail" likely originates from the practice of using doornails, which were large nails used in carpentry, particularly for securing doors. Once hammered in, the ends of these nails were often bent over, rendering them unusable and "dead." The expression suggests something that is definitively and irreversibly dead, emphasizing the finality of death in a vivid, relatable manner. The phrase has been in use since at least the 14th century, appearing in works by authors like Chaucer and Shakespeare.