You’ve undoubtedly heard the old line about how if each believer won one person to Christ each year (or month, or whatever) within a short time the whole world would be saved.
Why does this approach never work? Because of the limits of our social circles. We presume that everyone in the world is connected to everyone else. In fact, we are only loosely connected, with some having many connections and others having few. Information passes through the strongly connected ‘hub’ people, and they serve as gateways. They can stop the flow of information if they desire.
Thus while it is theoretically true that everyone is connected, in fact the non Christian world is cut off from casual relationships with much of the Christian world. Thus the in the each one win one scenario, Christians would pretty rapidly run out of people to win if they stay within their existing social networks.
Mission is about leaving ones existing social circle, and intersecting a new one. We are more comfortable with the idea of winning friends and family… And less comfortable with the idea of seeking out complete strangers. It is these disconnects–when people avoid other types of people–that cause the break down of world evangelization. Intentionally intersecting a new social circle is hard work but work that must be done.