This relates a bit to a quote by Chesterton which I put here some time ago.
The first (rule or maxim) is that the reader should neither agree nor disagree with an author until he is sure that he understand what the author is saying. To agree with what you do not understand is inane; to disagree in the absence of understanding is impertinent. Many readers start to disagree with what they are reading almost at once -- before they have performed the tasks of analysis and interpretation which should always precede that of criticism. In effect, they are saying to an author: "I don't know what you are talking about, but I think you are wrong." It would be just as silly for them to say, "right" as it is for them to say "wrong". In either case, they are expressing prejudice rather than undertaking genuine criticism, which must be based on understanding.
This rule calls for patience and humility on the reader's part. If he is reading anything worth reading -- anything which has the power to instruct him and elevate his mind -- he should be loath to judge it too soon, for it would be rash to presume that he has so quickly attained an adequate understanding of it. If he suspects that he has fallen short in his understanding, he should always blame himself rather than the author. Not only is that the proper attitude if the author is worth reading at all, but, in addition, such an attitude may keep the reader's mind on the task of interpretation. There is always time for criticism after that is well done.
I notice it also ramifies out to an interpersonal skill, as of course literary and topical discussion always seem to. The Catholic Church calls "rash judgment" the habit of leaping to conclusions -- usually negative ones, but I think it's possible to be too foolishly approving as well. Melancholics and cholerics (I'm one of the former) may be inclined to hit the negative side of the rash judgment, while sanguines and phlegmatics may be too quick to jump on a bandwagon.
Early teens are particularly likely to argue and to form hasty judgments, as you may remember from your own younger days or from life with teen children. This is a developmental advance of great significance, and is to be celebrated. The child is newly able to entertain abstract ideas and consider their meaning in his mind. However, he is not yet skilled in entertaining -- he pulls some in as HIS ideas, and rejects some cursorily, sometimes for very odd reasons, like not liking the author's name.
The goal of education is to foster the impartiality necessary to come to honest, not pre-digested, conclusions.
To some extent, of course, it's impossible not to evaluate as you go. I have met people, and books, that make me immediately wary on the first encounter. The trick is not to "rest your case" until you've thought it through. Nor ought you to start shotgunning your conclusions and judgments --like random pellets -- in all directions.
Since I'm a visual person, I usually think of reading a new book or entertaining a new idea as "letting it into the outer chamber". I try to entertain cordially, fairly, and impartially, but I keep it in the outside rooms until trust has been established. This is a process, and certainly doesn't come through hasty approval or hasty condemnation. As Hutchins points out, it is impossible to grow through reading and thinking if you just turn everything into yourself, as material to support what you already think and feel.
I doubt if many people succeed in doing this fairly and well ALL the time; it's an intellectual discipline. But I do think it's one of the more important habits to acquire, and it's one that each person must acquire for himself or herself. Once you can do it a bit though, you can truly be educated through books.