There are two dangers to be guarded against in old age. One of these is undue absorption in the past. It does not do to live in memories, in regrets for the good old days, or in sadness about friends who are dead. One's thoughts must be directed to the future and to things about which there is something to be done. It is unwise to be too attached to the youth in the hope of sucking vigor from its vitality. When your children are grown up they want to live their own lives, and if you continue to be as interested in them as you were when they were young, you are likely to become a burden to them, unless they are cold to you. I think that a successful old age is easiest for those who have strong impersonal interests involving appropriate activities. It is in this sphere that long experience is really fruitful, and it is in this sphere that the wisdom born of experience can be exercised without being oppressive. It is no use telling grown-up children not to make mistakes, both because they will not believe you, and because mistakes are an essential part of education. But if you are one of those who are incapable of impersonal interests, you may find that your life will be empty unless you concern yourself with you children and grandchildren. In that case you must realize that while you can still _ them material services, such as making them an allowance or knitting them jumpers, you must not expect that they will enjoy your company. Some old people are afraid of death. But in fact the best way is to make your interests gradually wider and ore impersonal. An individual human existence should be like a river-small at fist, rushing passionately past rocks and over waterfalls. Gradually the river grows wider and the banks move back and in the end they become mixed in the sea without any visible break. The old man who can see life in this way will not suffer from the fear of growing old and death. The author compares an individual human existence to a river because   _  .
Life is like a river, first small, and then it becomes wide life is like a river finally flowing into the sea old age and death are both natural just like a river old people will be mixed in the crowd like a river mixed in the sea