If you want to know someone’s true personality, play a game with them.

Related to the well-known (and wrongly-attributed-to-Plato) quote, “You can discover more about a person in an hour of play than in a year of conversation,” we have found one of the best ways to see inside a person’s personality: play with them.
It is during play that subconscious barriers fall; the walls we’ve spent a lifetime erecting come crashing to the ground once the element of structured playfulness is introduced. Play acts almost like hypnosis: we are inducted into the play gestalt and, by agreed consent, are all starting at a relatively common point. Once play begins, whether formalized or casual, we play to win.*
How people play these games reveals clear signs of their inner personality. Have you ever played Monopoly with your family? Then you understand. The hypnosis of the game lulls people into dropping their barriers; it puts the gatekeepers to sleep and lets loose the angels and demons within. Watch for the Cheater, the Negotiator, the Reconciler, the Appeaser. Watch, listen, and learn. When we sit down to play, it’s our inner selves who are rolling the dice and moving our mice (yes, a Mousetrap reference.)
*The goal of a game depends on what type of game is being played (see Finite and Infinite Games, by James Carse for a wonderfully detailed breakdown). Finite games, such as sporting games, are played in order to declare an agreed-upon winner. Infinite games (daily life activities, such as work, relationships, etc) are played with intent to continue the game (hence the term, “infinite”) and are lost only if the game comes to an end with the figurative or literal death of the player.

The Big Book of Improv Games – A compendium of performance-based short-form games