One day a young man went to the town and bought himself a new pair of pants. When he got home, he went to his room and put them on. He found they were about two inches(英寸) long. He went into the kitchen(厨房). His mother and his two sisters were doing some washing there. He said to them,“ The new pants are too long. They need cutting(剪) by two inches. Would one of you do this for me?” His mother and sisters were busy and nobody said anything.
   But after his mother finished washing, she went to her son's room and cut the pants by two inches. She came back without saying anything to her daughters. After supper, the elder sister remembered her brother’s pants. She went to his room and cut the pants by two inches without saying anything to anyone. The younger sister went to the cinema. But when she came back, she also remembered her brother's pants, so she went to his room and cut them by two inches, too.

近期，某校4名初中生相约在某一河边游玩，突然一名同学不幸滑入水中，其余3位同学发现后手牵着手去救他，结果一齐落水溺亡。这一教训警示我们（    ） 

下列观点中正确的是（　　）