I don't deny there is wisdom to be found from the books. The problem is some people take that wisdom literally. At times I hear someone "changing their whole life" after reading a single book. Usually it's not that dramatic. The change is something smaller, but still complete.
Change is good and sure those life changing stories are great. But reading one book and keeping it the highest authority of the subject afterwards is not the way. There is usually more than one view on the subject. The one you get from a single book is just one author's opinion of the matter.
People write from their perspective. Their situation and background could be completely different from yours or they might even have an agenda behind their words. It's a good idea to have some alternative views. Sometimes it might be that all the authors agree.
Another thing to consider the validity of the wisdom given in the book is the era it has been written. Some wisdoms might be eternal, but for most, the world changes and so do these wisdoms. What worked a couple of decades ago can already be outdated.