Dominoes are small rectangular blocks of wood or plastic marked with dots resembling those on dice. They are normally twice as long as they are wide, and each end of a domino has a value, or number, ranging from six to none (blank).
In a game of domino, the ends of two adjacent dominoes must match, which means one “touches” the other. When a domino touches another, it becomes an immediate candidate for being tipped. If it is tipped, the next domino in line will tip, and so on down the chain until all the dominoes have fallen. This simple mechanism is the basis of a great many games, which are often referred to collectively as domino. Some of these games are based on blocking, while others involve scoring points. In addition, dominoes can be arranged in complex geometrical structures, which is often very satisfying to observers.
Dominos are usually used in games for two or more players. Each player has a set of dominoes and turns over one when it is his turn to do so. He then places it in a position on the table where its end will touch the end of a previous domino, which must have a value equal to or greater than the number of pips on the touching ends of the exposed domino. When all the ends of the dominoes have touched, he scores according to the rules of the game.
A common domino set consists of 28 pieces: seven doubles (with the same number on both ends, from double blank to double six), and 21 singles (with different numbers on each end or a number and a blank). Many variations of the game exist; some are more complex than others. For example, a game called Muggins allows a player to score by placing a domino edge to edge against an opponent’s with the exposed ends matching: one’s touch two’s, five’s touch four’s, etc.
In fiction writing, the domino effect is a useful metaphor for plotting. As a writer, you must carefully consider what happens next in your story, and then create logical, plausible scenes that lead to that outcome. For instance, if your hero does something immoral, you must provide logic that gives readers permission to forgive him or at least keep liking him. If you neglect to do this, the story will fall apart.