Why Should I Keep My Drupal Site Updated?

Inspired by a recent conversation with a client, along with inheriting developer ownership of a few sites that were not kept up-to-date, here is a detailed explanation on why the code that runs your Drupal site should be updated and maintained.
Note that I'm talking about updating your site's contributed modules or core, which involves minor code changes (for example, updating Drupal core from 7.25 to 7.26), and not upgrading your site to the next major version (going from Drupal 6 to Drupal 7).

Why is Drupal so hard?

"But that's easy!" I say. "Make a view and have it be a page. Wait, no, that can be a bit confusing -- make it a block display instead." After installing Views and CTools, setting up a view, and giving a quick tutorial on block visibility, I'm reminded that it's really not so easy for someone unfamiliar with this system. So, why is Drupal so hard?

What is Web Development?

Web development is the more technical side of website building. Its tools run the gamut from the flashy user interfaces of Web 2.0 to command-line scripts reminiscent of DOS from yesteryear. Here's a quick overview of the core concerns of web development, along with some tools, products, and services involved in building and maintaining awesome sites.

What is Web Design?

The question "What is Design?" — Design with a capital D — is a question for philosophers and big-picture thinkers. My more practical worldview is that the design aspect of a project includes the whats of a website and the details of how the site should be presented to end-users.