This apparent contradiction occurs because people have two types of memory. Short-term memory can retain only six or seven items for up to a minute. Long-term memory can retain much more complex information for years and even decades.
Scientists have discovered that short and long-term memory are located in different parts of the brain. Short-term memory is found in the middle of the brain, but long-term memory is located all over the outer part. This is why, when a disease or stroke affects the inner part of the brain, and results in memory loss, the victim can remember events leading up to his memory loss, because they are part of his long-term memory, but cannot store new memories.
Psychologists know that memory is linked to the five senses. During the learning phase, a child who has reached the age of six has a vocabulary of 6000 words. Throughout the rest of his life the average person will acquire only another 14,000. Yet the foundations are laid before the can read, so he has learned these sounds by their meaning, rhythm and tone, and by association.
When information is held in the log-term memory, it is probably translated into some kind of picture and stored in the nerve cells in the outer part of the brain. There are more than 100,000 million such cells, each of which has 10,000 connections to other cells, making the network unbelievably complex.
The information in the cells is probably stored by chemicals which alter the way the cells work and the way they are connected to each other.
Something in a person's short-term memory can be transferred to his long-term memory by repetition and learning. The information is actually transferred by chemical messengers. These messengers are molecules which travel from one brain cell to another. Each molecule causes a specific action, and so 'transmits' a message.
So even though you may forget a telephone number you have just dialled, you can eventually store it in your long-term memory if you are going to need it in the future.