Note that the book itself contains 22 separate essays by different authors. This is part of the final one by Tyler Shores.
(This extract was actually much larger, and approved by the author, but I have reduced it to < 400 words since copyright is owned by the publisher.)

Paradox, Creation, and Memory

Inception is very much about the things the mind creates, ranging from fantastic, physics-bending displays of cityscapes folding on top of themselves to Cobb's guilt-driven projections of Mal. Cobb describes dream-building as "the chance to build cathedrals, entire cities, things that never existed, things that couldn't exist in the real world." Of course, we build dreams ourselves, but examining how we do so gives rise to yet more loops, and more paradox.

During one of the more provocative exchanges in the film, Cobb and Ariadne discuss the mechanics of creating a dream world, in which invention and discovery somehow become simultaneous operations.

Cobb: Well, imagine you're designing a building. You consciously create each aspect. But sometimes, it feels like it's almost creating itself, if you know what I mean.
Ariadne: Yeah, yeah, like I'm discovering it.
Cobb: Genuine inspiration, right? Now, in a dream our mind continuously does this. We create and perceive our world simultaneously. And our mind does this so well that we don't even know it's happening.

The idea of creating and perceiving something simultaneously seems paradoxical — especially if that perception is discovery. How can I discover something that I myself created? How, if I am creating my dream, can I be surprised by parts of it, and not know what will happen next? As Cobb sketches this idea—two curved arrows, pointing at each other's non-pointed ends—perceiving begets creation, which in turn feeds back into more creative ways of perceiving, and so on. Can the mind be both the subject (perceiving that which it creates) and object (creating the thing that it is perceiving) at the same time? Instead of being a paradox, perhaps this merely suggests that creation is less like a linear process of getting from one point to another, and instead is more like a feedback loop.

In Inception, characters are able to experience the contents of their dream experiences as they happen. For our own (non-lucid) dreaming experiences, we can only experience our dreams as remembered events when awake. In the film, Cobb blurs that line between the contents of memories and created ideas, which, as we find out, spells trouble.