I don't normally eat at McDonald's unless I'm really hungry and it's the closest place, but one month a year I make an exception: November. November is when they have their Monopoly-themed game.
The game has been running for at least a decade, and it's remarkably addicting to play. The reason, I believe, is that it short-circuits the player's capacity to work out how likely it is to win.
First, a quick primer on how the game works: On a variety of items that McDonald's sells, there are two pull-tabs, each one corresponding to a property from the classic Monopoly board game. In order to win, the player must collect all of the properties of the same color. Prizes range from $50 for Baltic and Mediterranean, the first two properties on the board, to $1,000,000 for Park Place and Boardwalk. All other property sets are trios save for the railroads, which are a quartet, just like the board game.
The clever piece of this game is that the players have limited information -- they're missing the information on the relative rarity of the various pieces. Each set of properties has two "common" pieces and one "rare" piece, allowing McDonald's to control the odds. The naive reaction to playing the game, however, is a carry-over from the board game: the player expects all properties to exist in the same proportion.
So, the player who collects a number of properties quickly works their way to having two-thirds of each of the sets, which sets off any number of involuntary reactions. The odds are suddenly in the player's favor! All they need is one more piece! And, of course, since the instinct is to assume equal distribution, they increase their visits, assuming that it can't be long until that final piece turns up.
Of course, the actual odds are no better (and in fact may very well be worse) than playing the lottery. The odds of winning the lowest prize ($50) are literally one-in-a-million; the grand prize's odds are "approximately" one in 542,034,000.
The online game is even worse. Here, the goal is the same: collect all of the same-colored property to win a cash prize. For every game piece code entered, the game "rolls" dice for you -- which, of course, seems egalitarian and random enough. After a moment's thought, of course, it's realized that it cannot be a fair roll; just try rolling a pair of dice and walking a piece around a real Monopoly board. All the properties are rapidly collected in just a few cycles, while on the electronic version, the "rare" properties get conveniently skipped by the dice rolls. There's no obvious fraud, of course, but the manner in which the game is apparently conducted contradicts what's actually going on behind the curtain, and it throws off the player's sense of the odds.