I once had a friend tell me, “people come into your life, and people leave your life, and that’s okay.”

Her theory is that some people are in your life to share wisdom and make an impact, and then they move on. While at that time, I thought it was somewhat profound to hear that, as I have grown in my profession, I now understand what she was saying.

The people we keep in our networks define us at every stage of our lives and careers. While we can lose everything—our cars, our jobs, and our homes—the people we keep in our lives will be there no matter what. And yet, many of us fail to see the value in understanding the network of connections we have, and the connections we are yet to build.

British anthropologist Robin Dunbar’s “magic number” theory has stuck with me over the years. He studied the size of the brain’s neocortex (the part of the brain that manages cognition and communication) relative to the body size of different specimens. He linked it to the size of the groups they could handle in their social system. And he believed the maximum number of relationships humans could maintain was 150 at any one time.

Today it is being argued that many factors may influence this number: personality, gender, extrovert vs. introvert status, social media participation (although we are seeing trends in social media for smaller, more select groups today), and many more. But by spending the past couple of decades managing my network, one thing is consistent. To manage, grow and nurture my network, I must have the time and desire to put forth the effort to make and keep these connections, and 150 seems right to me.

So how does this relate to Business Development? Well, very closely, since great business developers know the power of a great network. The question becomes, how are you managing your Fabulous 150 Network?

While the theory is nothing new, I think it is imperative to have BD teams spend time each year mapping and understanding who is in their network, which relationships need to be nurtured, and which relationships should be replaced (and by whom).

There are many forms of this exercise, but if you can imagine a target with four rings, then you have the basics. The very center of the target would represent your Loved Ones and Very Good Friends; yes, these relationships do take effort. Moving outward in the circle, the successive rings would be Friends (those who will call you back within a few hours); Meaningful Connections (those who will call you back within a few days—I find these are primarily professional relationships); and finally Acquaintances in the outer ring (people you recognize and who recognize you, but with whom you have no real relationship).

The next step is to sit down by yourself and start filling out names. (The first year you do this exercise is the toughest, and I suggest using your social media and outlook contacts.) Now, be honest with yourself; where do people really fit into your network?

Taking Dunbar’s magic number of 150 people, how does that fit your three inner circles: Loved ones and Very good Friends, Friends, and Meaningful Connections? The next part of the exercise is where good business developers excel. Who do I need inside my circles?  Who are the people I want to spend time with, who are willing to build a relationship with me? What is their value, and do they believe in reciprocity? And is it time to let go of certain people?

Unfortunately, the friend who offered her wisdom about people coming in and out of our lives is no longer a part of my inner circle, and that’s okay. Still, she provided me with the insight that being intentional with my network pays off in the long run, and in some way, that probably does make her a part of my forever network.

Doing this exercise as you make your yearly plans can provide you with specific goals when networking and creating your support team. Over the years, you will learn to build and love your own Fabulous 150 Network.