What is virality ?
Sometimes it feels like people believe virality is just magic pixie dust that can be sprinkled on anything. Fortunately, it’s much more concrete than that. But to understand how virality works, you first have to know that not all virality is the same. Many successful companies have done distinct things to help make their products go viral, all in completely different ways. So I thought it would be helpful to try to classify the disparate approaches.
I think this is the best article to understand how virality works, I could not say it any better myself:
The Five Types of Virality
and choosing the right one for your product to grownews.greylock.com