because the aural memory is weaker than the visual, as we have seen for ourselves in the tests which we have made.
maybe you should practice everyday with 'brain exercise' :
Learn something new. Pick up a magazine on dogs, for example, while you are waiting for the dentist. Scan the articles and relate what you learn to what you already know. If you are a builder you may discover how the home requirements of dog owners are different from others. You might expand your knowledge, but the purpose of this brain exercise is to train yourself to automatically look for connections between things. This helps you think more creatively. It also helps your memory, because having more connections makes it easier to recall things.
Here's a brain exercise you can use to help you concentrate better. You simply pay attention to what is going on in your head, and you resolve any little "mind irritations" you find there. If you feel stressed, there is a reason. Perhaps you never figured out where that book was that you were looking for this morning, and it has been quietly bothering you all day, just below consciousness. If you can become aware of all these stressors, small and large, and deal with them, you will feel more relaxed and have greater concentration and brain power in general.
Dealing with them doesn't mean you can resolve all these issues now. You can, however, do something with them so you can let them go for the moment. Write "find book" on your to-do list, and your mind will let go of the concern for now. Just bringing a problem to full consciousness and telling yourself something like, "There is nothing I can do about this until Friday," will often stop the unconscious worrying. After doing these brain exercises a few times, you'll find it becomes easier to recognize what is just below the surface, irritating you and sapping your brain power.
Try breathing deeply also. This shouldn't be classified with "brain exercises," but it can help. Get that oxygen into your blood, and into your brain. You can exercise your brain with hard riddles as well.