Latency is a design decision

We often treat performance as an engineering ticket to be filed after the design is approved. This is a fundamental error. Latency is not a technical byproduct; it is the texture of the interface.

When an interaction takes longer than 100ms to acknowledge, the user loses the feeling of direct manipulation. They are no longer moving the object; they are asking the computer to move it.

I recently audited a dashboard that felt 'sluggish'. The API response times were actually fine (200ms). The issue was the layout shift (CLS) occurring after the data loaded. The interface shimmered into existence, forcing the eye to re-focus.

We solved this not by optimizing the database, but by designing optimistic states. The button turns green immediately. The card assumes success. The interface lies, effectively, to preserve the user's flow state.