In such games, one gains gold by fighting monsters, performing tasks, and occasionally by randomly foraging in the world. The gold is then used to purchase armor, weaponry and training, making it easier to fight larger monsters, who hold more gold, and so on.
Every game has a point where one has gained so much gold from one's adventures that one can afford any item in the game, making the character exceedingly strong, and rendering all opponents ineffectual. This point is the cash Event Horizon. Usually, the later in the game this point appears, the more challenging the game is.