Spirit Airlines' shutdown after 10 years as America's ultra-low-cost carrier exposed how a business model built on radical cost-cutting became impossible to sustain when labor costs soared, fuel prices spiked, and larger competitors copied its playbook. The airline that democratized travel for working-class Americans ultimately fell victim to an unforgiving industry where small margins leave no room for error. Spirit Airlines introduced 'unbundling' to US air travel, charging separately for seats, carry-ons, and even boarding pass printing, which forced competitors to lower fares and became known as the 'Spirit Effect,' reducing airfares 5-10% at airports where Spirit operated.