Capacity markets pay generators for being available, not only for the energy they actually produce. Supporters argue that energy-only prices, even with occasional spikes, do not reliably finance plants that run few hours but are essential on peak days. A capacity payment, they say, is a way to buy an option on those hours without pretending that every megawatt-hour must carry the full capital cost. Opponents reply that a poorly designed capacity product can pay for plants that are not actually deliverable when the system is stressed: units with fuel-supply limits, or resources whose output is correlated with the very shortage they are meant to cover. They also worry that capacity payments blunt the scarcity signal that would otherwise attract demand response. The design fight is therefore less about whether reliability has a price than about whether the product being purchased is coincident with the hours in which reliability is scarce.