Tribes working cooperatively have been integrally to commerce from the surf system of the feudal middle ages, and the guilds of the Renaissance to modern day.
Fortunately our comfort with the size and number of our tribes has grown significantly beyond our nomadic/agrarian roots. Our DNA instinctual drive for belonging to the group is embedded in business processes today. In Reid Hoffman's new book, The Startup of You, he makes the point that our opportunities and business success comes from our networks e.g. tribes.
Networking inside or outside organizations requires meeting people you don't know and being able to talk about yourself and find out about them. I have executive clients with minimal footprint on Linkedin expect the perfect job posting to magically appear. Building a network is not learned behavior. Growing and advancing within a big company depends on who knows you and who gets to know and like you. Those whose networking fluency is weak or not a style fit for their company culture rail against the corporate "politics" they face when they should be getting better at networking.
Why is networking so hard? As much as we like to belong, we are hardwired in our DNA for a adrenal reaction of flight or fight that gives us a wariness, if not fear, of the new, the unknown, and change. Networking requires all of the above: we must change our behavior and reach out to unknown people to grow connections. It is an interesting DNA dynamic, we have move past our wariness of meeting new people in order to satisfy our drives to belong to a group (tribe).
I agree with Reid, that anyone who develops fluency in networking will up their success quotient in their careers because doors are opened by people you know.
The easiest first thing to do to grow your network is use Linkedin, Viadeo, and Xing to invite people to connect with you. It is a great start on instantly building your a base of hundreds if not thousands of contacts. The next easiest step is to start attending events: professional associations, conferences, trade shows and alumni groups to meet people.