When a request takes five seconds, the obvious question is what to make faster. The more useful question is what, precisely, the system spent those five seconds doing — or waiting to do. The answer may lie in unnecessary database work, excessive data movement, an execution plan, contention, or ...
Source: [Dev.to](https://dev.to/josemariairiarte/performance-engineering-what-is-the-system-waiting-for-483i)