Our brains work like computers: they input data and process it in accordance with their wiring and programming. Any opinion you have is made up of these two things: the data and your processing or reasoning.
When someone says, "I believe X," ask them: What data are you looking at? What reasoning are you using to draw your conclusion? Dealing with raw opinions will get you and everyone else confused; understanding where they come from will help you get to the truth.
