Every moment of every day, we are bombarded by information. For animals and prehistoric man, this information was always firsthand: the things one sees, hears, touches, tastes, and smells. With the advent of language, we gained access to another kind of information: secondhand. And in this information age, most of the data we encounter is secondhand.
Think about all the information that is in your head. This information - which you probably just call your memories - combines together in a cognitive framework to form what is called a worldview. Your worldview affects every single decision you make, and in many ways defines who you are as a person. But where did all the information which makes up your worldview come from?
Chances are, most of it was secondhand. Your parents told you, a friend told you, you learned it in school, you read it in a book, you saw it on TV, you overheard someone else's conversation. For the vast majority of this data, you probably can't even identify the original source. Yet should someone challenge a piece of this data that is in your head - even a minor piece - you will probably argue vehemently to support "your" side. But is it justified to do so? You have no idea where the original source was, whether it was correct to begin with, nor have you encountered any corroborating data since then. But most of us, in this situation, will passionately defend against any challenges of this information despite the lack of justification for doing so.
In today's world, the bombardment of information dwarfs that of our prehistoric and even historic ancestors. 24 hours a day, the power of mass media can become a virtual cacophony. Most of it is far from impartial (advertisements, for example) but we let it slip into our minds anyways, influencing future decisions and maybe changing the course of our lives. In many ways this has turned the world into a shouting match: whomever can yell a piece of information the loudest and the longest will eventually be believed, regardless of the merit of that information.
On consideration, this piecemeal and undisciplined process by which most people collage together their worldview seems a poor approach. For something as important as a person's worldview - on which they base all of their major life decisions, and indeed every decision they ever make - shouldn't the process be a bit better crafted?
There is a better way. It's called critical thinking.