The design, development and release of a complex website involve a large array of skills that few individuals can master all-together. In actuality, most successful web development efforts rely on a team of specialized individuals to cover the entire skill base.
Most people are in tune to the need for skill diversity. For instance, many people accept that the visual design of a website is often an artistic task performed by a graphic designer, while the configuration of a website is a technical process often performed by a code programmer.
The Drupal community has been working on an extensive breakdown of the skills that required for a solid Drupal development effort. You can study the breakdown from multiple angles using this clever chart:
Read more about the skill set breakdown, along with descriptions of each skill, and an ongoing discussion: