Eric Ries

The engine of growth is the mechanism that startups use to achieve sustainable growth

Sustainable growth is characterized by one simple rule:

New customers come from the actions of past customers.

There are four primary ways past customers drive sustainable growth:

2. As a side effect of product usage.

3. Through funded advertising.

4. Through repeat purchase or use.

Engines of growth are designed to give startups a relatively small set of metrics on which to focus their energies.

Therefore, companies using the sticky engine of growth track their attrition rate or churn rate very carefully. The churn rate is defined as the fraction of customers in any period who fail to remain engaged with the company’s product.

The rules that govern the sticky engine of growth are pretty simple: if the rate of new customer acquisition exceeds the churn rate, the product will grow

Growth happens automatically as a side effect of customers using the product. Viruses are not optional.