It is very comfortable to read stuff which we already know about. This is primarily because the brain doesn’t need to form new connections or destroy/modify older connections. There is an inherent inertia in the process of making cells or breaking/modifying brain cells. I think it’s just like physical exercise. The more changes your brain accommodates in less time, the more malleable it remains. Aah, it feels similar to lactose intolerance which I developed over this year. I went through a period of more than 3 months without drinking milk and now it is hard for my body to digest milk. Hmm, our mind is like a sword, which constantly needs to be sharpened, else it will become blunt. So, I think we should actively try to learn things which are HARD to understand for us. It keeps the mind active and sharp. Hmm, interestingly, a large number of physicists in the past have had some sort of inclination towards playing music. I think playing an instrument activates certain parts of the brain which take part in the creation of new ideas. Notable physicists who played instruments include Albert Einstein, Max Born, Werner Heisenberg, Richard Feynman and innumerable others. Learning to play music is SO DAMN HARD for adults that I’m sure it stretches your brain in countless ways.