APIs that external developers pay to use require more than good technical design. They require a pricing model that aligns cost with value, metering infrastructure that accurately tracks usage, and billing systems that translate usage into charges reliably. These are product and engineering concerns that compound — a poorly designed pricing model produces integrators who spend more time managing API costs than building their product, and metering infrastructure that loses events produces disputes and lost revenue.

An API that works in development and fails in production in ways you cannot diagnose is worse than an API that fails loudly. Production is where assumptions meet reality, and the gap between them only becomes visible if you can see what is happening inside the system. Observability is the discipline of making distributed systems understandable — building in enough visibility that when something goes wrong, you can find out what, where, and why without guessing.