You get a job because of your brother-in-law. You land that big sale because your high-school buddy is the director of product management. That first venture into the world a mobile apps gets a big boost when your college roommate, now a famous investor, tweets out the link a few times.

Yes, it's who you know.

The question is: Why does that work so well?

It's something I've been thinking about, especially after reading some new research by Robin Dunbar, the guy who invented the Dunbar number. His original theory is that we can only maintain about 150 good relationships. As an aside, I've always thought this was one of the reasons a startup sometimes fails, because the founder can only have so many friends. Once a small firm grows well beyond 150, he or she just can't maintain the same quality of relationship (or control).

I wrote about this problem already, but Dunbar's new research suggests that the 150 number doesn't work online. Many of your "friends" on Facebook would not really care if something bad happened to you. Only about four of them would get involved and only 13 would express sympathy, on average. The rest would ignore you. It doesn't matter if you have 150 of these "friends" or 2,000. My takeaway is that an online friend is only a percentage equivalent of a real friend.

That has big implications in every area of business. Who you know is so important because real friends actually care about you. It's why many of us go to conferences. It's why it's so important to have lunch meetings. It's why you have to get out of the office once in awhile, set down the phone, and look people in the eyes.

As we move into a digital existence where tech is even more ubiquitous, the "who you know" issue will keep coming up. If you don't really know anyone, you might not see as much success or land any big contracts. Knowing people online doesn't really count. There are a few exceptions, of course. I tend to think extroverts in real life have better relationships online, because they are constantly making new connections, chatting on Facebook, and tweeting out links for friends.

However, there's something about having a deeper relationship in person. Your friends see your body language, they see your expressions, they see your happiness and pain. They can tell if you've been eating properly. Empathy is mostly an analog undertaking. Forming business connections in real life is important because people will know what you're thinking and feeling, not just what you're typing. And, they will remember you when they find out you have a new company or need help.

What are the implications? First, it should drive your decisions almost every single day. A recent article in the New Yorker made this point: You'd think with the advent of Skype and video-conferencing that people would start flying less, but they are flying even more. My view is that many of those passengers know they have to be physically present at the Toledo sales conference or do that product demo in person. They know that no one will ever invest in your startup if they never meet you in person.

I had an amazingly serendipitous experience once. I was at the CES conference in Las Vegas many years ago, before I started writing here. It was late at night at a meet-and-greet event, and I was tired. I sat down at a table and started chatted a little with the other tired journalists. One of them was complaining that she had just lost one of her writers. I asked a few questions, found out about her experience and the magazine, and made a contact. Later, she emailed me and we eventually formed a working relationship that lasted about 5-6 years. I can't imagine what would have happened if I had skipped CES that year or hid in my hotel room.

A word of advice here: Get out there and make contact with people, even if it's inconvenient or awkward. Develop deeper business relationships. Ask an investor to lunch. Then, do it again. The "who you know" model works because people have a tendency to care about people they know. They look for people to help; they want to lend a hand. If you are not physically present, they will ignore you.