Yes, a game can demonstrate a person's nature if you watch it from the side for a long time. But I must say that in order to get a full impression of a person, you must watch him in the gym or gambling for a long time. A single game may not reveal all sides of his nature. In addition, this condition is extremely important, you must behave naturally. The author in the start post wrote about a mafia boss who offered to play a game of chance to observe the nature of a person. I am afraid that such a game would hardly demonstrate his character. After all, it was a single, one might say, random game and in this game the person sought to demonstrate the best features of his character from the point of view of the mafia boss, and not to behave naturally.