Having a solution come at a cost is one method worldbuilders use to keep magic, special abilities, or powerful new technologies from fundamentally changing their world in ways they do not want or cannot entirely predict. By linking fantastic abilities or events to a great cost and/or sacrifice it limits how often they can be performed. If a wizard can transmute any metal to gold, the economy crumbles (or shifts). If a healer can bring a person back from the dead then murder, duels, and war may be far more likely outcomes of any disagreement. If genies and wish spells exist, reality itself may be rewritten each hour and no one would ever get any work done. However, if all these abilities and events come at a great cost, then their relative impact is lessened because they become rare events.

This cost may be physical pain or exhaustion, a sacrifice few are willing to make, a highly elaborate ritual or lengthy manufacturing process, or some other limiting factor.