• Inventing new protocols, data structures, and algorithms to solve problems no one else has tackled before • Designing and writing low-latency, high-throughput Java systems from scratch • Tuning memory usage down to the byte, and measuring performance down to the nanosecond • Writing parsers, interpreters, and other core infrastructure from first principles • Mentoring senior and staff engineers while leading complex technical initiatives • Creating tools and profilers to measure and improve execution across the stack • Making design decisions that will affect the architecture and correctness of a publicly visible ledger • Switching fluently between system-level design and single-instruction-level optimization • Building tests and harnesses that help ensure nothing ever breaks, ever