In every school there is a 'top'crowd that sets the pace, while the others follow their example. Let's say the top crowd decides that it is smart to wear bright red sweaters (毛衣). Pretty soon everybody is wearing bright red sweaters. There is nothing wrong with that, except the fact that for some people bright red is rather unsuitable. The situation can even become dangerous, if the top crowd decides that it is smart to drink or to drive cars at seventy miles an hour. Then the people who follow the example are putting their lives in danger. They are like sheep being led to the slaughter (屠宰). Now, it is likely that you have come across situations like these more than once in your life. In fact, it is likely that at one time or another you probably did something you knew to be wrong. You may have excused yourself by saying, 'Gee, the crowd does it. ' Well, let the crowd do it, but don't do it yourself. Learn to say'No'. Develop your own standards and your own judgments. If you know the crowd is planning something of which you disapprove, have the courage to bow out gracefully. You' 11 have the satisfaction of standing on your own two feet. The main idea of this passage is that______.