Which pricing innovation, first systematically implemented by King Gillette for razors, became known as the 'loss leader' strategy that revolutionized modern retail?

Pricing strategies have evolved dramatically throughout retail history, with certain innovations fundamentally changing how products reach consumers. This particular pricing innovation revolutionized retail by making products more accessible to everyday consumers while simultaneously increasing store traffic. Though seemingly obvious today, this concept was a groundbreaking discovery when first implemented systematically in retail.

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The razor-and-blades model (selling the base product at/below cost while profiting on necessary refills/accessories)
The psychological pricing method (pricing items at $9.99 instead of $10.00)
The subscription-based pricing model (charging recurring fees for continuous product access)
The dynamic pricing strategy (adjusting prices in real-time based on demand and competition)