What makes people irrational thinkers?

[vulcanlogician]

One thing I have learned from teaching math is that logic isn't a natural way of thinking. Even those who have an aptitude have a LOT of difficulty when it comes to coming up with and writing logical proofs. Although we like to claim that logic is the 'laws of thought', in reality, most conclusions most people arrive at are not found through logic.

Instead, people usually have intuitions that they then use some sort of 'reasoning' to justify. But the reasoning is usually NOT the reason they believe. it is the way they justify their intuitions. And their beliefs are based on those intuitions, not on logic or reasoning.

From Economist Daniel Kahneman:

Kahneman divides our thinking into two subsystems: type 1 and type 2. Type 1 thinking is fast, intuitive, unconscious thought. Most everyday activities (like driving, talking, cleaning, etc.) make heavy use of the type 1 system. The type 2 system is slow, calculating, conscious thought. When you're doing a difficult math problem or thinking carefully about a philosophical problem, you're engaging the type 2 system. From Kahneman's perspective, the big difference between type 1 and type 2 thinking is that type 1 is fast and easy but very susceptible to bias, whereas type 2 is slow and requires conscious effort but is much more resistant to cognitive biases.

https://news.ycombinator.com/item?id=4102848

"Resistant" being an operative word here. We are never free of cognitive bias. But we aren't helpless slaves to it either.

I agree with you that we are not essentially logical beings. I like Plato's allegory in Phaedrus where he likens us mentally to a chariot with three parts. Two horses and a charioteer. One unruly horse (desire), One obedient horse (emotion), and our rational inclinations (which are represented by the charioteer). Looking at that whole model, you can see that we as people are pretty much 95% emotion and desire-- when accounting for raw power... what really motivates us. Plato never thought that we should be more reasonable than we are desirous or emotional. In fact he considered it impossible. (One of the few matters Plato is decidedly correct on.) Rather, he thought the best role for our reasonable nature is to try it's best to keep the two horses on track as best it could. Only our more passionate nature can actually propel us forward through life. Our reasonable nature can do naught but try and steer as best it can.

Or, put another way by the Lebanese poet, Gibran:

 Your reason and your passion are the rudder and the sails of your seafaring soul.
    If either your sails or your rudder be broken, you can but toss and drift, or else be held at a standstill in mid-seas.
    For reason, ruling alone, is a force confining and passion, unattended, is a flame that burns to its own destruction.

https://poets.org/poem/reason-and-passion

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As for thinking being "rearranging our prejudices." A bit too cynical, maybe. But I'm sure that's what we're doing some of the time when we think. Maybe even most of the time. But, taking into account Kahneman's distinction. I think we can "escape" our prejudices when we employ type 2 thinking. But type 2 thinking itself can't always do the job either. We need dialectic to finish the job. We need our ideas to be opposed by a disagreeing party, or a Socrates... something... to rouse us out of self-satisfaction.