Stopping Mechanism

Type
Friction

Intent
Reduce the effectiveness of a mechanism every time it is activated.

Also Known As
Law of diminishing returns

Motivation
To prevent a player from abusing a powerful mechanism, the mechanism’s effectiveness is reduced every time it is used. In some cases, the stopping mechanism is permanent, but usually it’s not.

Applicability
Use a stopping mechanism when:
 * You want to prevent players from abusing particular actions.
 * You want to counter dominant strategies.
 * You want to reduce the effectiveness of a positive feedback mechanism.

Structure


Participants
 * An action that might produce some sort of output
 * A resource (energy) that is required for the action.
 * The stopping mechanism that increases the energy cost or reduces the output of the action.

Collaborations
For a stopping mechanism to work, the action must have an energy cost, produce resources, or both. The stopping mechanism reduces the effectiveness of an action mechanism every time it is activated by increasing the energy costs or reducing the output of resources.

Consequences
Using a stopping mechanism can reduce the effect of a positive feedback loop considerably and even make its return insufficient.

Implementation
When implementing a stopping mechanism, it is important to consider whether to make the effects permanent. When the accumulated output is used to measure the strength of the stopping mechanism, the effects are not permanent. In that case, it requires players to alternate frequently between creating the output and using the output in other actions.

A stopping mechanism can apply to each player individually or can affect multiple players equally. In the latter case, the game will reward players that use the action before other players do. This means that the stopping mechanism can create a form of feedback depending on whether leading or trailing players are likely to act first.

Examples
A subtle stopping mechanism can be found in the timber-harvesting mechanism in Warcraft III. In Warcraft III, players can assign peasants to cut wood and produce lumber. Because the peasants have to transport the lumber back from the forest to the player’s base and cannot cut wood while transporting, the distance to the forest has an effect on effectiveness of the production mechanism. Because cutting wood clears the forest, the distance increases as the player cuts more and more wood.



The price mechanism of the fuel market in Power Grid involves a stopping mechanism (see below). In Power Grid, players use money to buy fuel and burn fuel to generate money. This positive feedback loop is counteracted by the fact that buying a lot of fuel actually drives up the price for all players. Because the leading player acts last in Power Grid, this stopping mechanism causes powerful negative feedback for the leading player.



Related Patterns

 * Stopping mechanisms are often found in systems that implement Multiple Feedback.
 * A stopping mechanism elaborates the Dynamic Friction pattern.
 * A stopping mechanism might be elaborated by a Slow Cycle pattern.