A few thoughts about teaching the exact sciences at an advanced stage (perhaps even earlier? debatable). I find that in some disciplines (especially maths!) linear and step-by-step teaching is given extreme importance. Writing things down very very logically is considered the correct way when teaching in the class rooms. I think this is actually harmful. Students might get used to such presentations and then when it comes to thinking about a problem, they often try to analyse and think in the same logical and linear fashion. This is highly undesirable! Problems are not solved by thinking linearly! Analysis yes, but not problem solving. One often has to relate to several different concepts and draw intuition from other problems that people have solved. This means that you might be forced to jump from one idea to another, try out bold conjectures based on some intuition and so on. Many of these paths will fail but they will add to your intuition about the problem. And it is this process that one must try to teach students. This is not easy. It means that when the teacher lectures, he/she will not complete arguments, often will not provide all the details in one go and most importantly, may not give the complete picture immediately. The teacher will state the goal clearly and then wander around a bit, experiment with ideas and try to convey why some approach works the way it works. This will entail quite some work on the part of the student. It will also leave you confused till you see the whole picture. A good teacher will do this so that you vaguely see the direction but not so much that you will sit back and watch the teacher do all the thinking instead of you.
The benefits of this process are that albeit hard, it does teach you to think on your own with suitable guidance from the teacher. It also conveys the message that solving your own problems is not going to be anything like just learning a subject from a book.
This also is precisely why we need teachers. Books are good to learn subjects linearly. But they rarely convey the intuition behind the subject. A teacher can show us how to read between the lines in a book.
To conclude, linear presentations are over-rated.