Computer networks, he has come to believe, are so dauntingly complex that loopholes will always remain. Blame human beings, error-prone by definition. Though programmers are often regarded as akin to sorcerers, they are as bungling as any non-gearhead. There are an average of five to 15 bugs in every thousand lines of code, which means that Windows 98 is riddled with somewhere between 90,000 and 270,000 oopsies. People are basically pretty helpful, and they'll rarely think twice about cheerfully responding to a well-written request.
People are also woefully lazy.
Humans can be excused for their foibles. The book's real spleen is reserved for the various snake oils that are passed off as anti-hacker panaceas. Schneier ably debunks the magic-bullet claims of every class of product. Too easy to fool with forged requests for access. Too many false alarms.