This refers to the fact that people- this sounds like something you probably already know but it has been documented by psychologists.

指的是人们...,照字面意思,可能你们已经猜到,心理学家已经证明了这一原理

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For example, people tend to believe that their team will win; this has been documented by psychologists.

比如,人们倾向于相信他们支持的球队会赢,心理学家已经证明了这点

耶鲁公开课 - 金融市场课程节选