16. When it comes to having perfect memories, it is clear that we humans must have had some faults in our blueprints! Why don't we remember everything that we want to remember? It can be frustrating and disheartening. Sometimes it can even cause us to lose self-esteem or others to think less of us. Truly, though, we are all forgetful. If we weren't, diaries would never be kept, secretaries would never be hired, and the "Blackberry" would not have been invented!
Most of us have vivid memories of our lives from about age three to our present ages. These are stored in what we call our "long-term memory". What about before age three? Sigmund Freud discovered the fact that we forget most of our early childhood. Psychologists disagree on what causes this amnesia, and the investigation (调查) has been going on since Freud's time. A very good theory, born from the results of experimentation with babies, is that absence of language ability at the time of an event stopped us from describing it to others. The memory exists in our minds, but words were not associated with it when it happened, and therefore, it doesn't become a subject in our adult autobiographies. There are some exceptions, but these are rare.
The other kind of memory, the "short-term memory", is what we are usually referring to when we say, "I forgot" Experts say that you can keep about seven things in your memory at once for up to three days. During that time, you may forget something in order to put something else in its place, or you, believe it or not, put it into long-term memory. What goes into short-term memory are things you've learned about recently, in the past day or two. Only if something really remarkable happens does it stay in your short-term memory for longer. For instance, you may have met your favorite celebrity last week, and this week you can tell all the details to a friend. A simple example to illustrate your short-term memory is to look at a list of twenty words for a minute or two. You will discover that you cannot remember more than about seven of them and that they are the ones in the beginning and at the end of the list (because your mind has judged them to be more important than those in the middle).