I’ve been thinking a lot about the friendships and relationships I have in my life. Specifically about the concept of Dunbar’s Number, which is the assertion by the well-known anthropologist Robin Dunbar that a human can only maintain a limited amount of stable relationships. Dunbar gauged the number of relationships to be between 100 to 250.

Let’s just use the commonly quoted 150 number to make things easy.

Another way to think about this is you have at maximum 150 people in your life. Everyone else will remain a part of the gray background of strangers. The people you walk next to in a city but never know. These 150 people will be your parents, your significant other, your kids, your siblings, your neighbors, your roommates, your sorority sisters, your coworkers, and the guy who always hooks your burrito up at Chipotle.

Imagine what your Facebook would look like if you could only have 150 friends. Pretty small, right?

All of the depth of your life will be packed into this small subset of the world’s population.

This set of people is largely chosen early on in life, by the geography of where you live, what your parents value, and what you were interested in as a kid. If your dad liked football, he probably had you go out for the team, where you made friends as a result. You might still keep in contact with some of these people, even if you don’t see them very often.

A study published in Royal Society Open Science showed this pattern of friend accumulation persists until the mid-twenties, where people then start to actually lose friends. A large part of that being the birth of children, which places a heavy burden on maintaining friendships.

One of the tools I was taught to analyze relationships with is Social Penetration Theory. This communication theory basically states that people are like onions in that they have varying layers that they expose to one another, and over time, your social interactions become deeper and deeper.

Your progression through the layers of someone else’s onion is in direct proportion to the depth you have in that relationship.

After recently attending a friends wedding, I realized that I can have a significant amount of depth in a friendship that will not be maintained or even referenced for months on end.

My friend and I can pick back up from where we last left off, with large chunks of time in between the interactions. I would say that this is a normal phenomenon, surely most humans on the planet experience this with one or two people in their lifetime.

However, this is the exception, not the norm. Most relationships have to reach a certain level of depth before they can be maintained with little to no contact.

What seems important to this exploration is that the further down into the layers of the onion you go, the less maintenance you have to do on the relationship in order to keep it smoothly running.

This is made even easier with social media because you can be an incidental witness to life events of another person without actually being there. The better you know someone, the easier it is to jump back into life at the same pace as before.

These relationships are assigned spaces on the caste system of your Dunbar Hierarchy. Over time these people either move up or down the tiers based on the time and energy you choose to invest with them. The lower echelons will be replaced at a more rapid rate.

This is how you can go from being very close with someone to not recognizing them. They rolled down friendship mountain and became a snowball you do not know.

Since you can’t be friends with everyone, can you pick friends who are going to improve your life?

Can you make your Dunbar Hierarchy a tool for self-improvement?

We have all heard the platitude that you, “become the average of the 5 people you spend the most time with.”

If you spend time with five broke people, you’ll be the sixth, etc. etc.

You will become the lowest common denominator of the people in your Dunbar Hierarchy. If you maintain lots of relationships with low-level drug offenders, you’ll likely catch some jail time. If you spend a lot of time with people who work out obsessively, it’s hard to be out of shape.

Humans are creatures of habit. By extension, the people you spend time with help form and create the habits you repeatedly do. Both of mind and of action. I rarely see someone who is conservative spending loads of time with a group of progressive friends.

This is not to say that you should never spend time with people who do not contribute to your life. Volunteering is a great example of that variety of time expense, and yet it is one of the most fulfilling things a person can do.

The way I look at friendships is something I learned from Tai Lopez. I have three-minute friends, three-hour friends, and three-day friends. Each level of that scale is in relation to how they affect my life. If I know they will persuade me into getting wasted at a bar, I don’t let myself spend three hours with them. Conversely, if I know we will have a good discussion about finances, I am much more willing to spend three hours with them.

Take a look at who you spend time with. Are they someone you would trade lives with? If they aren’t a person you would gladly swap bodies with, what affect is their life having on yours? You will reflect the surroundings you give yourself. Choose wisely.