Explaining the Idiom "Dead as a Doornail"

You've heard the phrase "dead as a doornail" before, but it never made much sense, because all inanimate objects are just as dead. Besides, doors are now more likely to be held together with staples and glue than with nails. Maybe whoever coined the phrase just liked the alliteration. But there's more to it than that.

This video starts off talking about the phrase, but fairly quickly turns into a chapter in the history of carpentry. It has to do with the particular challenge of joining flat slabs of hand-hewn wood side-to-side to build a door, back when nails were hand-made. The video ends up being way more interesting than you expect. -via reddit