阅读短文，并按照题目要求用英语回答问题。
When I was in primary school, I got into an argument with a boy in my class．I have forgotten what the argument was about, but I have never forgotten the lesson learned that day．
I was convinced that "I" was right and "he" was wrong --- and he was just as convinced that I was wrong and "he" was right．The teacher decided to teach us a very important lesson．She brought us up to the front of the class and placed him on one side of her desk and me on the other．    
In the middle of her desk was a large, round object．I could clearly see that it was black She asked the boy what color the object was．"White," he answered．
I couldn't believe he said the object was white, for it was obviously black! Another argument started between my classmate anytime, this time about the color of the object．
The teacher told me to go to stand where the boy had been standing and told him to come to stand where I had been．We changed places, and now she asked me what the color of the object was．I had to answer, "White．" It was an object with two differently-colored sides, and from his viewpoint it was white．Only from my side was it black
My teacher taught me a very important lesson that day: You must stand in the other persons' shoes and look at the situation through their eyes in order to truly understand their perspective（观点）．
What is the main idea of the text? （No more than 10 words）
What is the meaning of the underlined words "was convinced" in Paragraph 2?
（No more than 3 words）
What did the teacher ask the students while changing positions?
（No more than 8 words）
Why are both of their answers right? （No more than 10 words）
What do you think of the teacher? And why? （No more than 20 words）