High intelligence isn’t always immediately obvious.

Have you ever heard the expression, empty vessels make the most noise? It’s not always true, but it is true that often, people with the most intelligence talk the least.

There are several reasons for that.

Sometimes, for example, intelligent people can be very shy.

Other times, they may simply prefer to listen and observe while other people talk.

Then, there’s the issue of the communication range, the theory that effective communication becomes difficult or impossible between two people whose IQs are too far apart – usually more than about 30 points or so.

In other words, the smarter a person is, the fewer the people they will have around them that they can have meaningful conversations with.

Basically, there are lots of reasons why intelligent people may avoid talking too much. And often, these people have other traits in common, too.

1) They question everything

One of the most noticeable traits of an intelligent person is their skepticism.

I don’t mean they don’t believe anything they hear. But they tend to think rationally and logically about any new information they get and compare it to what they already know to determine whether it’s true.

This skeptical process ensures that smart people often have the best possible information and the most well-thought-out opinions of anyone you’re likely to meet.

But it can also make conversation with less intelligent people tricky.

Think about it: imagine being surrounded by people who uncritically believe whatever they’ve heard on the news, social media, or from their friends.

You want to point out that they may be wrong, or that they aren’t using their reason to determine whether their views are correct or not.

But often, when you do that in conversation, people get defensive. It’s easy to offend someone when challenging their views, even if you don’t mean to.

For an intelligent person, it’s often easier to stay silent than to question the people around them.

2) They listen more than they talk

It’s a fact that intelligent people are often more interested in receiving than broadcasting.

Partly, that’s because they love to learn new things and take in new information.

Also, because they like to think logically, they want to make sure they have all the information they can possibly gather before making a statement or opinion.

The result is that smart people are often more comfortable listening to others than they are talking themselves. They recognize that every conversation is an opportunity to learn something new, so they will often keep silent and let others speak so they can learn more from them.

3) They think logically

We all like to think that our thoughts are grounded in logic and reason. The reality is, for most of us, emotion defines what we think about the world around us.

So many people believe what they want to believe, interpreting the world through the lens of their own feelings, rather than trusting in evidence to help them decide what to think.

However, intelligent people tend to think more logically than the rest of us.

Psychology professor Art Markman points to a study which found that “one consequence of IQ differences is that they lead people to focus on different kinds of information. People with higher IQ scores find it easier than those with lower IQ scores to keep in mind the abstract structure of an argument, and so they naturally focus on structure. As a result, their intuitions when faced with an argument are based on the structure of the argument.”

In other words, intelligent people think about what people are saying in a way that leaves their emotions out of it.

This is an extremely valuable trait to have. But because it’s different from how most of us make decisions and evaluate arguments, it can make logical people feel out of touch.

Often, the end result is that they prefer to keep their logical opinions to themselves.

4) They have good self-control

Intelligence is a great thing to have in life, but it doesn’t guarantee success. As some studies show, having a high level of self-control can be just as important, or even more so.

Brain science tells us the prefrontal cortex is responsible for many different higher cognitive functions that we associate with intelligence. But it is also linked with self-control.

In other words, intelligent people have brains that are better at controlling themselves and their actions.

What does this mean for conversation? Well, it means that intelligent people are less likely to blurt out the first thing that comes into their head. It also means they are less likely to react emotionally to what other people are saying.

This greater level of self-control is a useful trait in many ways. But it often means that intelligent people tend to stay silent while other people are getting caught up in the emotion of the moment.

5) They enjoy being alone

Let me introduce you to the savanna theory of happiness.

This theory states that what makes humans happy today is often things that would’ve made our ancestors happy when they were trying to survive on the African savanna.

So it’s not just the consequences of your actions that matter. It’s also what the consequences would have been in the wild environment humans first evolved in.

Living in a densely populated urban environment, for example, makes us less happy, just as it would have for our ancestors.

But the research on this theory also suggests that the effect is much stronger for more intelligent people.

Also, the research shows that frequent social interaction make most people happier. But when it comes to people with high IQs, the opposite is actually true.

Smarter people are happier when they spend more time alone.

Maybe it’s because they can spend more time thinking about their own ideas in silence. When you realize that, it’s not hard to see why smart people may be more likely to stay quiet around others.

6) They prefer deep conversations

Of course, it also depends on what you talk about.

A person with a highly capable brain will naturally have deeper and more profound ideas about the world and their place in it. And it can be hard to put those ideas to one side and instead talk about more shallow subjects that most people prefer in casual conversation.

The truth is, a smart person may have no idea about the latest celebrity gossip or what was on TV last night. But most people aren’t ready to discuss quantum mechanics or neuroscience when they first meet someone.

So sometimes, if a smart person is staying quiet, it may be because the conversation you’re having isn’t the kind of conversation they prefer.

Get a smart person talking about an intellectual interest, and you may have trouble getting them to shut up.

7) They are self-critical

Being intelligent often means being analytical. And intelligent people don’t spare themselves from their own logical and merciless analysis.

Paradoxically, this can often mean that the smarter a person is, the more self-critical they are. Because they expose themselves to the work of the greatest minds in human existence, it’s easy for an intelligent person to start to feel insecure in a way that less intelligent people rarely do.

To put it simply, smart people know exactly the limits of their own intelligence.

This habit of self-criticism can be bad for a person’s self-esteem. So sometimes, a smart person may stay quiet because they feel they have nothing to contribute to the conversation.

8) They are obsessive about their interests

Great achievement in any pursuit requires dedication and a borderline obsessive tendency to focus.

This is a trait intelligent people often have more of than people with more average intellects.

Sometimes, smart people will get fixated on a particular passion or interest. It might be the mysteries of outer space, the intricacies of human psychology, or abstract mathematical problems.

When you get deep into a subject, you often lose touch with other people, at least a little.

Having a consuming passion occupies a lot of your time and cuts you off from more mundane interests. It can become harder to talk to other people who don’t share your interest in your particular field of expertise.

9) They don’t like to argue

How often have you really changed someone’s mind an in argument?

Personally, I’m not sure I ever have.

Smart people are well aware that once you start arguing with someone on a subject, it’s easy for people to get defensive and refuse to change their views, even when proven wrong.

So when people are saying things an intelligent person knows to be untrue, often, they will simply keep their mouths shut.

They may know more than the person who is speaking. But they are probably also aware that criticizing people’s views often leads to an emotional argument which an intelligent person would rather avoid.

Sometimes, it’s better to say nothing at all.