“But I never ever even when using textbooks stuck to only one textbook.” This made me smile. I have the same habit. I never go deep into a topic without adding a second source. Books are just a material copy of a course given somewhere. It’s not the books (or the fact of writing) which is problematic but this belief that many people have that printed matter has a greater authority than knowledge shared for free on Internet. Textbook offer a scaffolding of what is to be learned and that’s good to indicate a possible route toward what i want to learn. I want to stay in control of where I will really go. That’s why I add a second source and keep an eye on both as I progress in understanding. In other words I’m keep control on the compass and the compass box. I call this being an “Independent Learner”, which is different from rebel, or self-directed. I don’t want anyone to tell me what to think or even influence or drive for me. I suspect you are one too 🙂