I think this may be confusing for a new person to grasp, it was hard for me to grasp as well. I'll do the best I can.
We want to attract experts
The main site ServerFault.com has specific guidelines on what types of quesitons can be asked by the community, which is governed by the community. There are a lot of reasons for this. Mainly, this site wants to attract experts in the field. To do that, when the said expert visits the site, she does not want to have to peel through questions about
- What books are good for learning about VPNs?
- How do I setup a VPN?
- What does 'VPN' stand for?
- When would I use a VPN?
These are basic questions that a VPN 'expert' would typically know already. Now, a site with VPN experts would naturally attract VPN beginners looking to get some advice. Please realize that
Beginners are encouraged to come as well
However, asking questions without researching first is not respecting someone's time, and makes one look bad (more on that later). Search engines have come a long way over the past 20 years, and there is a Wikipedia article on pretty much everything. Also, try searching the main site for the vpn tag, chances are someone has asked a couple of basic questions in the site's history that will supplement Wikipedia or any book you read.
That book sucks
Next, everyone learns from different books in different ways. What may be a good book for one person, may not be a good book for another. This will lead to biased voting on any said questions, long comment chains, and general flaming. Granted, the community is good about cleaning this stuff up, no one wants more work for themselves, as our mods are apart of the community. A general rule of thumb is: Chatty questions should be taken to chat, and product recommendations, books or otherwise, are chatty questions.
Most here are not Anti-n00b
I haven't talked with anyone here I can remember that is against an OP that is learning a new technology or (dare I say it) helping sysadmins in an area that is new to them. As a matter of fact, one must continue to learn new technology in this industry in order to stay current, valuable, and marketable. One main thing that separates a professional sysadmin from a wannabe though, is the professional spends their own time first to actually research the problem or new topic. Among other things, it's a bad look when another admin can type your exact error message (or question) in Bing and the first result solves your problem (gives you an answer). I know from experience, most learning questions can be solved using $SearchEngine, and if/when you come across conflicting information, then it's time to take it to the experts for clarification. It's all about helping yourself first.
Now, that should answer this meta question about why 'learning materials' being off topic. As for your book question, feel free to take it to the chat, if you're brave enough. Muha,MUha,MUHAHAHAHAHHAAAAAA.