Darwin pointed out that if you take one pair of breeding elephants and make some conservative estimates about their fertility, you would have more than 15 million elephants in less than 500 years (if none of them died an early death.)*
It's pretty clear it doesn't work that way. Perfect viral growth, even slow viral growth, rarely happens. If it did, we'd have an elephant problem.
The same thing happens with your idea. If one person told four and the cycle repeated itself for a few generations, everyone would know about it. But they don't. It tails off. One person often tells zero. Or people hear about it but forget.
Real viral growth comes from one of a few likely paths:
- Someone sneezes your idea with amplification. They show up on Oprah, or you have $100 million to spend on ads. Great work if you can get it...
- The idea spreads with fidelity. One person really does tell four, and there's not a lot of leakage. Starbucks worked this way, largely because the chain grew at just the right rate and kept its character as it did.
- The idea is particularly 'viral' (using a popular understanding of the word.) One typical person doesn't tell four, she tells 400. This is the blogger effect--lots of small amplifiers, working in unison.
- The idea lives a very long time and spreads slowly. In our rapid-fire world, this one is pretty rare.
It's possible to combine some of these tactics. When a political candidate starts out, for example, it's almost certainly with a grassroots approach, but then, perhaps, once enthusiasm picks up, he or she shows up on TV. You can organize around this and plan for it, but you certainly can't guarantee it.
Here's the big news: it doesn't matter much how many elephants you start with. In other words, big launches don't necessarily scale. What matters is how fertile your elephants are (number of babies per generation) and how long they live. If Darwin's elephants managed to squeeze in just one more generation, they end up with 30 million.