If you do not use your arms or your legs for some time, they will become weak, and when you start using them again, they slowly become strong again. Everybody knows that. Yet many people do not seem to know that memory works in the same way. When someone says that he has a good memory, he really means that he keeps his memory in practice by using it. When someone else says that his memory is poor, he really means that he does not give it enough chance to become strong. If a friend says that his arms and legs are weak, we know that it is his own fault. But if he tells us that he has a poor memory, many of us think that his parents may be blamed, and few of us know that it is just his own fault  . Have you ever found that some people can't read or write but usually they have better memories? This is because they cannot read or write and when they have to remember things, they cannot write them down in a small notebook. As a result, they have to remember days, names, songs and stories, so their memory is being exercised the whole time. So if you want to have a good memory, learn from the people: practice remembering things in a way as other people do. Few people know that if someone has a poor memory it is   _  .
his own fault his parents' fault his teachers' fault his friends' fault