It has become a practice among many students (compared to a few decades back) to read only what is taught the day and not what happened before. Though it is a good practice to start with current topic, revising back to the beginning as much as possible is very much helpful in performing well in exams. Every time you repeat, the mind seeks new meanings and interpretations and this becomes helpful while answering the HOTS questions (If you have the determination to answer every question to the best of your ability & beyond!) When we read again and again new questions related to the topic arises in our mind and the effort to answer the questions is the beginning of true learning. Only when you read with an active, curious and questioning mind, learning becomes effective. And don’t rest until you find satisfying and convincing answers to your questions… The answers, the explanations and the logical reasoning developed by you will last forever. But always discuss those with a good teacher. Sometimes it happens that the explanations developed by oneself has some faulty considerations and may be violating the basic principles of conservation or some other of the sort.