Guy Kawasaki quotes Seth Godin (from his new book “Small is the New Big”):
For an idea to be spread, it needs to be sent and received.
No one sends an idea unless:
1. They understand it.
2. They want it to spread.
3. They believe that spreading it will enhance their power (reputation, income, friendships) or their peace of mind.
4. The effort to send the idea is less than the benefits.
No one gets an idea unless:
1. The first impression demands further investigation.
2. They already understand the foundation ideas necessary to get the new idea.
3. They trust or respect the sender enough to invest the time.
Notice that ideas never spread because they are important to the originator.
Notice, too, that a key element in the spreading of the idea is the capsule that contains it. If its easy to swallow, tempting, and complete, its far more likely to get a good start.