Influence, do we have too much?

Why do we read text books? It is interesting to think of a text book as a valid opinion in certain subjects, considering that the book is in one authors opinion. Isn't that book then biased? Why are we reading and being examined on one persons perspective of a subject when we are supposed to be getting the unbiased truth? I guess, if this is true, all of the "facts" about anything we have ever learned are influenced from what ever source we are getting the facts from. If so is anything we have been told, technically the whole truth? Or is it just a version of the truth with a twist of numerous influences? And since that twisted truth has been passed down a tweaked from person to person how do we know what we are being taught in real its original content?