WOW, subjectivism has gone wild at Three Sources. Howard, I think being brainwashed is a form of insanity so that is probably a good analogy. As JG noted, OPAR gives the best answer to this question that I have read but I will give it a try. Start with the nature of human beings. Human beings use their minds to interpret physical stimuli. The physical universe exists regardless of how I interpret it. However, the closer I come to interpreting it correctly, the more successful I am.

For example if I am insane or brainwashed into believing that I can fly, I will jump off a building and die. (Hopefully, before I reproduce.) For human beings to exist as a species, this kind of disconnect with reality has to be eliminated for the majority of people.

Let’s look at the other end of the spectrum. If I am a genius and my understanding of reality is better than someone else’s I have a survival advantage. For this reason, I choose always to think about what I know and examine my premises in light of whatever data comes in (i.e. take the red pill.) I contend that a man can not be easily brainwashed as long as he does this. Of course, this is contingent upon a continuous supply of valid evidence, which is why censorship and ignorance are so destructive: They are the tools of brainwashers. Physical evidence directly perceived can only be misunderstood by the perceiver and not distorted by others.

In short, you cannot be brainwashed by reality, only by other people.