Agreed. I'm actually not sure if what I should take away from that introduction is "This material seems easy but isn't, so go through everything carefully even if you think you understand it" or the opposite: "If this book seems easy, it's not advanced enough for you and you already know everything; so read something else instead."
I took it as meaning the second. There's even a recommendation as to what else to read; a book on Lisp.
Another monthly installment of the rationality quotes thread. The usual rules apply: