Only if you don't know the book. Even then, I explained it in the next line (single point of vulnerability). But I can see that if you read the first sentence

Only if you don't know the book. Even then, I explained it in the next line (single point of vulnerability). But I can see that if you read the first sentence in isolation, and didn't know about the book, it could be interpreted as rude. It wasn't meant as rude. I'm sorry that it came across as offensive to you, and so I clarified in my follow up. BTW: They're excellent books (the second in the series is best IMO).