Here's how it developed:
* Card Games: In card games, having a full deck means you have all 52 cards. A complete set is necessary to play the game properly.
* Missing Cards: If a deck is missing cards, it's considered incomplete or "not full." This can affect the game's outcome and make it unfair.
* Metaphorical Use: The idea of a "full deck" became a metaphor for a person's mental faculties or intelligence. Someone with a full deck is considered to have all their wits about them.
* Incomplete Deck: Someone "not playing with a full deck" is seen as lacking intelligence, being illogical, or having a limited mental capacity.
The phrase likely gained popularity in the early to mid-20th century, reflecting the cultural understanding of mental capacity at the time. It's important to note that the phrase is now considered outdated and potentially offensive, as it can be used to stigmatize individuals with disabilities or mental health conditions.