Why intuition fails more than half the time, how Amdahl's law caps every speedup you can ship, and the measurement loop senior engineers run before touching a line of code.
A hot path is a function the profiler finds over and over. Five shapes (CPU, allocation, cache, lock, syscall), one diagnostic loop, and the hardware counters that resolve ambiguity — from junior intuition to senior TMA.
An O(N) scan on contiguous memory routinely beats an O(log N) tree traversal — because cache lines, prefetchers, and branch prediction dominate wall-clock time in ways big-O cannot model.
Why one screen renders into 200 database queries, the four fix patterns (JOIN, IN, batch-loader, prefetch) with their tradeoffs, and how the same problem repeats across REST, gRPC, and microservice fan-out.
Putting it together: performance as a discipline, not a project
Seven tools, one loop. Profile, classify, fix, verify, enforce. The loop is what makes performance a durable property of the team, not a one-time project.