I recommend The Complete Walker to newcomers who've never backpacked when they seem all at sea as to how to start learning what they need to know. They often plead ignorance and seem intimidated by all the details, without knowing how to sort them out.

The book approaches gear using a very simple organization principle of comparing a tent to a bedroom, cooking gear to a kitchen, and so on. This demystifies what gear is supposed to accomplish and relates it to common knowledge. A newb is likely to feel comfortable with this approach.

Secondly, Fletcher has a relaxed attitude about nature and just likes walking around outdoors. There is little gushing or romanticism in his discussions, but a deep appreciation for simplicity, with a large added dose of curiosity about his surroundings. This is an excellent attitude to inculcate in newcomers, who often have overwrought fears or overly romantic expectations about wilderness walking.

In short, reading TCW as a first introduction to backpacking will put a newbie on a sound footing that will help them make the leap into trekking with good habits and a helpful way of thinking about all the details of how to hike and camp in the backcountry. Once you've internalized these, you don't need to read it a second time to relearn these lessons.