Have you ever been afraid to talk back when you were treated unfairly? Have you ever bought something just because the salesman talked you into it? Are you afraid to ask a boy (girl) for a date? Many people are afraid to assert themselves (insist upon their own rights)．Dr．Robert Alberti, author of Stand Up' Speak Out, and Talk Back, thinks it's because their self-esteem (自尊) is low．'Our whole set-up makes people doubt themselves,' says Alberti. 'There's always a 'superior' around—a parent, a teacher, a boss—who 'knows better'．' But Alberti and other scientists are doing something to help people to assert themselves. They offer 'assertiveness training' courses (AT). In the AT courses people learn that they have a right to be themselves. They learn to speak out and feel good about doing so. They learn to be aggressive (敢闯的,有闯劲儿的)without hurting other people. In one way, learning to speak out is to overcome fear. A group taking an AT course will help the timid person to lose his fear. But AT uses an even stronger motive—the need to share. The timid person speaks out in the group because he wants to tell how he feels. AT says you can get to feel good about yourself. And once you do, you can learn to speak out. In the passage, the writer talks about the problem that______．