This talk covers the methodical process used to design a high-performance, specification-compliant logging API for OpenTelemetry Go. It explores the journey from early prototypes to production-ready implementation, highlighting key challenges like achieving zero allocations on the hot path, balancing user-friendliness with performance, and designing APIs that evolve gracefully as specifications change. Beyond OpenTelemetry, this talk shares practical lessons and reusable techniques for anyone designing complex APIs or performance-critical libraries, showing how evidence-based decisions, benchmarks, and documentation can guide sustainable design.