the.com/dead end

means A passage, path, or course of action that goes nowhere further and simply stops.

from Straightforward compound English, first used literally in the 1800s for a street or passage that terminates with no outlet — a road that's 'dead' because it carries you nowhere new. The figurative sense, for a plan, job, or line of thought that leads to nothing, followed naturally in the same century, as people realized life has plenty of cul-de-sacs that aren't made of pavement.