We read and reread a chapter in a book, yet a few minutes later, we forget it! This is usually caused by lack of attention, as the experience does not make a proper impression upon us.
Forgetting is also due to lapse of time between an experience and the attempt to recall it. As a result of normal metabolic process of the brain, a memory trace tends to fade or decay with the passage of time, unless we renew it by repeating the experience which gave rise to it. Thus, it is advisable to recall what has been read after a gap of 10 minutes to reinforce the memory trace.
If the memory trace formed is left undisturbed, it gets consolidated, and can resist interference. During the process of consolidation, however, the memory trace is still susceptible to interferences from matter learnt subsequently. This simply means that we tend to forget a certain thing not only because we learnt it a week ago, but also because we have learnt other things during the week.
Amazingly, it has been found that we forget less in sleep than while we are awake. For example, a person who reads a story before going to sleep, Amazingly, it has been found that we forget less in sleep than while we are awake. For example, a person who reads a story before going to sleep, would be able to remember many details when he wakes up. Thus, after reading at night, it is advisable to revise immediately after waking up, to reinforce the memory trace. Again, there is always a conflict between the wish to experience, and wish not to remember it! There is also a process of unconscious forgetting of painful memories, known as repression. Such memories may not be recalled, because of the sense of anxiety or guilt which they could provoke. Thus, we tend to remember events which give us satisfaction, and forget those which annoy us! - Dr. J.N. Reddy