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 same banks issuing high-interest credit cards offer substantially cheaper personal lines of credit to customers with identical FICO scores. Despite being a logical tool for consolidating expensive card debt, these products receive almost no marketing, making them largely invisible to consumers.

The massive 100x return on investment for card issuers like Amex and Chase makes them insensitive to the card's cost. This dynamic protects Composecure's high margins and discourages issuers from switching to cheaper, lower-quality suppliers for their most valuable customers.

Instead of paid marketing, Nubank scaled to over 120 million users with a customer acquisition cost of just a few dollars. This was achieved organically through word-of-mouth, fueled by a superior value proposition (no fees, better service) that solved a clear and painful consumer problem, enabled by a 20x more efficient cost structure.

While many assume high credit card rates cover default risk, actual charge-offs on revolving balances average only 5.75%. This is a significant cost but accounts for less than a third of the typical interest rate spread, indicating that other factors like risk premiums and operating costs are major drivers.

By engineering your model so that the gross profit from a new customer in their first 30 days exceeds your acquisition cost (CAC), you can fund marketing on an interest-free credit card. The customer's own payment repays the debt before interest accrues, creating a self-funding growth loop.

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.

While lower interest rates seem appealing, they often fuel intense market competition and bidding wars. Higher rates can thin the herd of buyers, providing an opportunity for those who can still afford to purchase to secure a deal with less pressure and more negotiating power.

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.