Why does someone say 10-4 on the radio to mean yes?

The phrase "10-4" originates from the ten-codes used in Citizens Band (CB) radio communication, which were developed to provide clear and concise messages. "10-4" specifically means "message received" or "understood," effectively signaling agreement or affirmation. It became popularized in the 1970s and has since entered common vernacular as a way to indicate acknowledgment or consent.