Drupal is a powerful and flexible platform to build websites with rich funcionalities without building almost anything from scratch. This flexibility brought by the usage of a powerful framework and the work of a super active community can abstract people to understand what is Drupal doing behind the scenes.
Most of performance talks regarding Drupal focus on aspects like infrastructure changes, caching strategies, and comparison of performance between modules or platforms. Unfortunately when performance problems occur, development teams also follow several strategies to replace several aspects in their platforms, jump directly to look for slow queries before trying really to understand where is the bottleneck.
However, most of the times what really needs to be done is to look to what the application is doing and understanding why is it taking so long to do it. Drupal is a platform used by million of websites worldwide and its performance is easy to measure and compare.
At Acquia we have done dozens of performance assessments, and even if we usually face the same problems, sometimes we found weird situations that are only possible to be detected when measured. Measuring and profiling is the only way to understand performance problems in a site and provide valid fixes.