我曾看到这样一篇文章：一位教师上公开课,找一名学生到黑板上去做练习题。学生一共做了五道题,做完后,教师问下面的同学：“他做得怎样?”同学们几乎异口同声地说：“最后一题做错了!”这位教师说：“为什么你们只看到了他做错的那一道题,而没看到他做对的四道题呢?” I have seen such an article: A teacher in open class, to find a student to the blackboard to do exercises. The students did a total of five questions. After the teacher asked the following classmates: “How did he do that?” The students said almost unanimously: “The last question was wrong!” The teacher said: "Why do you guys only Did you see the four questions he did wrong?