Emerson was an American poet and philosopher that talked about individualism and that people should not accept help from anyone else and on this, one of his beliefs was that you should not focus on learning what you can find on books that is knowledge from the past and instead of that, look for the thruth in your heart.
According to that, the answer is that the drawback of relying too much on books according to Emerson is that they make you focus on the knowledge from the past instead of looking for the thruth in your heart.
