Our world is populated by all kinds of people with hugely varying levels of intelligence. Almost anyone would consider themselves to be intelligent, of course, and it can be very hard to get an accurate assessment of our own intelligence. After all, our thoughts always tend to sound smart in our own head, don’t they?

And intelligence is very important. Especially in a professional context, a smart and agile mind can be your best asset. But people who are less smart often have habits that out them as stupid and can also be quite catastrophic in a number of circumstances.

These are the five most fundamental differences between smart and stupid people.

1. Stupid people blame others for their own mistakes

It’s very noticeable, unprofessional, and something a smart person would never do. If you consistently try to foist your mistakes off on others, you demonstrate to everyone that you can’t be the sharpest tool in the shed.

Stupid people don’t like taking responsibility for their mistakes. They prefer to wallow in self-pity or just go straight to playing the blame game.

Travis Bradberry, author of the bestseller "Emotional Intelligence 2.0.", knows how telling this behavior really is.

"It's never a good idea to cast blame. Be accountable. If you had any role — no matter how small — in whatever went wrong, own it," Bradbury advises in a guest contribution for "Inc.". "The moment you start pointing fingers is the moment people start seeing you as someone who lacks accountability for his or her actions."

Smart people also know that every mistake is a chance to learn to do better next time. A neurological study conducted by Jason S. Moser of Michigan State University has shown that the brains of smart people actually react differently to mistakes.

2. Stupid people always have to be right

In a situation of conflict, smart people have an easier time empathizing with the other person and understanding their arguments. They are also able to integrate these arguments into their own chain of thought and to reconsider their opinions accordingly.

A sure sign of intelligence is the ability to look at and understand things from a different point of view, and intelligent people are open minded towards new information and changing parameters.

Stupid people on the other hand will continue arguing forever and will not budge from their position, regardless of any valid arguments brought against them. That also means they will not notice if the other person happens to be more intelligent and competent.

This overestimation is called the Dunning-Kruger effect. It is the cognitive bias that makes less competent people overestimate their own skills while underestimating the competence of others.

The term was coined in 1999 in the publication of David Dunning and Justin Kruger. The psychologists had noticed in prior studies that in areas like reading comprehension, playing chess or driving a car, ignorance leads to confidence more often than knowledge does.

At Cornell University they conducted more experiments on this effect and showed that less competent people don’t just overestimate their own skills, they also don’t recognize when someone else’s skills are superior.

Dunning writes: "If you're incompetent, you can't know you’re incompetent.… [T]he skills you need to produce a right answer are exactly the skills you need to recognize what a right answer is."

Of course this does not mean that smart people always think everyone else is right. But they listen attentively and consider all arguments before making their decisions.

3. Stupid people react to conflicts with anger and aggression

Obviously even the smartest people can get really angry from time to time. But for less intelligent people this is the go-to reaction whenever things aren’t going their way. When they feel like they don’t have control over a situation as much as they would like, they tend to use anger and aggressive behavior to secure their position.

Researchers of the University of Michigan conducted a study on 600 participants with their parents and children, over the span of 22 years. They found a distinct correlation between aggressive behavior and a lower IQ-score.

The researchers wrote in their elaboration: "We hypothesized that low intelligence makes the learning of aggressive responses more likely at an early age, and this aggressive behavior makes continued intellectual development more difficult."

4. Stupid people ignore the needs and feelings of other people

Intelligent people tend to be very good at empathizing with others. This makes it easy for them to understand another person’s point of view.

Russel James of the Texas Tech University conducted a representative study with thousands of Americans and found out that people with a higher IQ are more inclined to give without expecting anything in return. As it turns out, an intelligent person is better at assessing the needs of other people and also more likely to want to help them.

"People with higher cognitive ability are better able to understand and fulfill the needs of distant others."

People who are less smart have a hard time imagining that people could think differently than they do and would therefore disagree with them. Also the concept of doing something for someone without expecting a favor in return is more foreign to them.

Everyone is selfish now and again, it’s completely normal and human. But it’s important that we keep the balance between the need to pursue our own goals and the need to consider other people’s feelings.

5. Stupid people think they are better than everyone else

Intelligent people try to motivate and help others. They do this because they are not afraid of being overshadowed. They have a healthy level of confidence and are smart enough to accurately assess their own competence.

Stupid people on the other hand tend to badmouth others in order to look better themselves. They believe themselves to be above everyone else and are always quick to judge. Prejudice is very much not a sign of intelligence.

In a Canadian study published by "Psychological Science", two scientists of the Brock University of Ontario found that "people with low IQs tend to be more in favour of harsh punishments, more homophobic and more likely to be racist."

Many biologists believe that the human ability to cooperate has been instrumental to our overall development. That could mean that the most important signifier of intelligence is being good at working with others.

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