I've not read the book (yet) but I have read a couple of reviews and it sounds like Seligman appreciates that there is a time for pessimism as well as optimism.
"Unlike many self-help books, there's no bad-mouthing of pessimists here. In fact, Seligman describes studies that seem to prove that pessimists are much better at seeing the world as it really is. ...
... The author explains how to balance optimism and pessimism and when to listen to each voice, though of course it could take a lifetime to perfect this process."
Here's one http://www.goodreads.com/review/show/40033602.
"Unlike many self-help books, there's no bad-mouthing of pessimists here. In fact, Seligman describes studies that seem to prove that pessimists are much better at seeing the world as it really is. ...
... The author explains how to balance optimism and pessimism and when to listen to each voice, though of course it could take a lifetime to perfect this process."