Well, you don't.
You don't have to take it from me, either. Psychologists, sociologists, anthropologists, and philosophers have been looking at this for a long, long time, and almost all of them agree. You are easily tricked.
You are frequently deluded, manipulated, and led to believe all manner of things, and not only from outside influences, either. You do it to yourself.
So, if you are truly open-minded, the most important thing to take on board is that your open mind could probably do with some sort of security system, because it's letting in a load of bollocks.
I consider myself to be a very analytical person. In fact I've been accused of being too analytical, and on occasions it's a fair comment. Sometimes I spend more time asking why than living in the moment. I am very solutions-oriented, which is obviously useful but not always what people need from me. I started asking why as soon as I could talk, and if anything, I've got worse with age.
But even I can be tricked, deluded, and manipulated because I'm human. What I'm saying is, if it can happen to me, it can happen to anyone.
There are several reasons for this. One, logic is not absolute. Even if the decision being made is regarding numbers, decisions are rarely purely mathematical. If that were the case economists would never disagree, anyone who could add up would be a billionaire, and businesses would never fail. You may have noticed, this is not the case. Two, the calmest people on the planet still have emotions. If you have emotions, you can be manipulated. Three, if you are relying on memory you're going to be fooled. Human memory is very, very fallible.
It won't help you to decide that you are not going to be tricked, because it happens at a level you are not aware of, deep in your subconscious. HIDDEN. The human mind is an amazing thing, but some of it is just not accessible. If you don't believe me, the next time you can't remember somebody's name, or how to spell a word, or where you left your keys, please, do tell me where that memory is stored. I rest my case.
And, you know what? It's OK. You don't have to be totally sharp all of the time. Nobody can expect that, and you can forgive yourself for the occasional screw-up.
But sometimes these delusions are long-lasting, all-encompassing, and what's more you will try to defend and justify them. And they can be very harmful.
An example of how they can be harmful to you is often referred to as low self-esteem, which really means lack of faith in your own abilities. If you believe you are worthless, or useless, or stupid, or ugly, or whatever it becomes a self-fulfilling prophecy. If you believe that nobody likes you, it will happen. If you believe that you can't do X, you'll probably fail at it. And yet these are all delusions.
On the other hand if you believe that people (any group, or any individual other than yourself) are bad, evil, wrong, lesser, dangerous, or any negative at all, it can lead to that person or those people being harmed, by your delusion. This is where prejudice, oppression, and bigotry are born, and there is no limit to the harm this can do. It can lead to genocide if the delusion is shared.
You don't have to be mad to be delusional. I had a fascinating discussion yesterday about phobias. A phobia is essentially a delusion that you can be harmed by something that cannot really harm you. And this can be a real problem in your life, or in the life of people around you. It can lead to great harm. But anyone can be phobic, despite being perfectly normal otherwise. It's a pocket of irrationality in an otherwise rational mind. Because ALL minds have the potential for irrationality.
The only thing close to a solution here is awareness, and it guarantees nothing. But it's better than inertia, and I strongly recommend awareness as a stratgey to improve your life, and the life of others too. You can call it mindfulness instead if you are so inclined, it only matters that you think about it at all.