Performance Optimization Is Not a Guessing Game

The most common performance optimization mistake is optimizing without measuring. Developers have notoriously bad intuitions about where bottlenecks live. We overestimate the cost of function calls and underestimate the cost of memory allocation and cache misses.

Profile first, then optimize. Identify the hot path — the 5% of code that consumes 95% of execution time — and focus your efforts there. Optimizing cold code is wasted effort that adds complexity without measurable benefit.

After optimizing, measure again. If you cannot demonstrate a measurable improvement, revert the change. Optimizations that do not move the needle are just additional code to maintain.