A team spends three weeks rewriting a hot loop in Rust bindings, shaves forty milliseconds off a function that runs once per request, and ships it. The page still takes four seconds to load. Nobody profiled first. That’s the pattern behind most performance work that goes nowhere: real effort, wrong target.

Optimization only pays off when you know where the time actually goes, and that’s rarely where intuition points. Developers tend to suspect their own code, because that’s the part they wrote and the part they can picture running slowly. The database, the network, the third-party API call buried in a middleware layer — those stay invisible until you measure them.

Performance optimization is the area of mobile development most susceptible to the wrong kind of effort. Teams spend significant engineering time improving benchmark numbers that have no correlation with user experience while ignoring the specific failure modes that cause users to uninstall apps and leave negative reviews. The gap between what is easy to measure and what actually matters to users is wide, and navigating it requires a more careful choice of metrics than most teams make.