GE employs a razor-and-blades model on an industrial scale, accepting losses on initial engine sales to powerful airframers like Boeing. This secures a multi-decade, high-margin stream of mandated service and parts revenue from a fragmented base of airline customers, where aftermarket sales can be 3-5 times the original engine price.

Contrary to the common perception of users paying off balances monthly ("transactors"), the majority—about 60%—are "revolvers" who carry debt. This group is the primary source of profit for card issuers, as they are subject to interest rates now averaging a staggering 23%.

The payment card market has a stable, recurring revenue base. Of the 4 billion new cards issued annually, most are replacements for expired or lost/stolen cards, not net new accounts. This provides a durable, predictable demand floor for manufacturers like Composecure, independent of new customer growth.

Despite investor focus on its well-known distribution business, Amadeus's Air IT division (inventory, reservation management) now generates 50% of group profits. This less visible, mission-critical software segment is the company's most profitable and formidable moat.

A surprisingly large portion of high credit card APRs covers operating expenses, particularly marketing. Issuers like Amex and Capital One spend billions annually on customer acquisition. This spending is passed directly to consumers, as higher marketing budgets correlate with higher chargeable rates.

Overbooking isn't a flat algorithm. Business routes are overbooked more heavily due to flexible traveler schedules, while leisure routes with fixed plans (like a festival) are a huge risk to oversell, as almost everyone shows up. It's a lesson in understanding customer context to manage risk and revenue.

Affirm's CEO argues the core flaw of credit cards is not high APRs, but a business model that profits from consumer mistakes. Lenders are incentivized by compounding interest and late fees, meaning they benefit when customers take longer to pay and stumble.

Airlines are increasingly devaluing elite status by offering last-minute cash upgrades to non-status members via mobile check-in. This practice allows them to monetize empty premium seats, often leaving their most loyal, high-status flyers stuck at the top of the upgrade list in economy.

The system of charging retailers an interchange fee (around 1.8%) that is then passed to consumers as rewards (around 1.57%) creates a strong network effect. Consumers are incentivized to use rewards cards, and retailers cannot easily offer discounts for other payment methods, locking both parties into the ecosystem.