It's quite funny... I just finished an online blitz game and I thought I performed the game quite well. However, upon turning on the silicon machine, Fritz immediately discovered that my opponent was winning with a huge advantage of over +3.00!! It so turns out that my opponent had missed a vital move and played what seemed like a natural human move which shrank his advantage from +3.00 to an instant 0.00 in 1 move and then -1.10 in the next move - shocking to say the least.
However, I have to admit that the winning move was quite difficult to spot. He had put my king under immense pressure and had continued to check my king, inadvertently missing a zwischenzug (an in between move) that didn't involve a check which would have won the game 2 moves later.
This is one problem I had (not with respect to the book) while reading the book from Charles Hertan on Forcing Chess Moves in which he discusses zwischenzugs on Chapter 8. In this chapter, while Hertain explains the importance of always looking for zwischenzugs, in practice, it is EXTREMELY difficult to spot and near impossible to calculate if you're calculating rather long variations in your head.
Even World Championship matches have been decided because of this important tactical motif. A case in point, in Game 12 of this year's match between Topalov and Anand - Topalov had evidently missed 34....Qe8 when he started the tactical complications starting with 31. exf5 but not Anand. If a 2800 rated player can miss it, what chance is there for us mere mortals? :)