There knowledge we gain from books is
There are many sources of acquiring knowledge, for example books, teachers, experience.
We can learn about different things from our teachers or by reading books but we also need experience to use the provided. Books are an invaluable treasure of knowledge, nevertheless, the knowledge we gain from books is incomplete without experience. Experience plays an important role in our life. For example, a car driver who learns all the signs and rules and passes the written test cannot just simply drive a car, he has to learn how to drive on the road. So practical experience will help him to drive a car.
The knowledge we gain from books is written by different authors. They write their ideas and concepts in those books and we get the opportunity to read them. However, by experiencing the things written we find out whether those ideas were true or false. We read books and compare them with our lifetime experiences and see that there are situations that are the same but how to overcome these challenges can only be learnt by experiencing it.
To conclude, books give us limited knowledge, whereas experience teaches us what is right or wrong.