Seth Godin:
Notice that ideas never spread because they are important to the originator.

Notice too that a key dynamic in the spread of the idea is the capsule that contains it. If it’s easy to swallow, tempting and complete, it’s a lot more likely to get a good start.

For an idea to spread, it needs to be sent and received.

No one “sends” an idea unless:

a. they understand it

b. they want it to spread

c. they believe that spreading it will enhance their power (reputation, income, friendships) or their peace of mind

d. the effort necessary to send the idea is less than the benefits

No one “gets” an idea unless:

a. the first impression demands further investigation

b. they already understand the foundation ideas necessary to get the new idea

c. they trust or respect the sender enough to invest the time

This explains why online ideas spread so fast but why they’re often shallow. Nietzsche is hard to understand and risky to spread, so it moves slowly among people willing to invest the time. Numa Numa, on the other hand, spread like a toxic waste spill because it was so transparent, reasonably funny and easy to share.

More here.