The best programmers are lazy programmers. Drupal, more than many other systems holds that maxim to be true. Why do lazy programmers have an advantage?
Because Drupal is not a traditional software framework. It is a framework, but it is a community first and a framework second. There are over ten thousand existing modules to choose from and thousands more blog posts and online resources to copy code from. Add to that a thriving community on IRC channels, forums and commercial support companies like Acquia and there are many ways to find solutions. The last thing you should resort to is writing custom code.
Custom code is expensive to maintain, risky to a project and creates a dependency on the people who wrote it. So while it is necessary to write some code on the vast majority of large Drupal sites, strive to practice configuration before coding. You can accomplish a lot just by picking the right modules and configuring them to suit your needs.