根据以下内容回答题：
All of us rely on what we see．We say to ourselves，“I know，was there；I saw it hap-pen．”And that seems to settle the matter．Or does it?Can we really trust the evidence of oureyes?Take competitive sports．Fans who see the same will not agree with each other and will the disagree with the referee(裁判)．“He was out of bounds when he caught the pass，”says one fan．Says another，“You are crazy．I saw it with my own eyes．He was five feet in bounds．You must be blind．”The referee rules that the receiver did step out of bounds．But thousands of fans are still not convinced--because they were there!
It’s the same story in the courtroom．Trial procedure depends on witnesses giving sworn testimony．But just how reliable is the testimony of a person who repots what he has seen?In a recent study，ten thousand witnesses were asked to describe the man they saw commit a crime．The study reveals that，on the average，the witnesses overestimated the man s height by five inches，his age by eight years，and gave the wrong hair color in 83 percent of the cases．These witnesses didn’t play tricks on them!
What can we do to keep error to a minimum?First of all，don’t let your emotions interfere with your vision．Don’t see something because you want to see it．Se．condly，try to stay relaxed．If you are tense，you are likely to see red when the color is blue．And finally，it helps to make notes of what you see．Don’t rely on your memory alone．Take pictures，make recordings，and use any other aid to reduce distortion．
The main idea of this passage is that__________． 查看材料