The world of technology is shifting its center to applications. That means everything from operations to networking is trying to enable a more application-driven or application-aware or application-X model of delivering network and application services. While it looks elegant on a slide comprised of the three "tiers" of an application, the reality is that an application world is highly complex, massively integrated, and very confusing.
Not to surprise you, but even this is greatly simplified. The complex web of interconnections that makes up the "middle" tier of an application can be so confusing it requires its own map, which architects often design and tack to walls to be able to see "the big picture" in much the same way DBAs will map out a particularly complex schema to understand the relationships between tables and objects and indexes.
The resulting diagram of a real environment would be, by anyone's standards, unreadable in digital format.
And that is why it's easy to say, but really super mega ultra hard to do.