For a product to grow mostly by itself, what important capability should it offer users?

The most important capability a product should offer users for it to grow mostly by itself is to facilitate and incentivize user-driven growth. This capability is commonly known as virality, which means the product is inherently designed to spread among users through their interactions. For a product to grow mostly by itself, its existing users must be empowered and motivated to bring in new users, creating a self-sustaining cycle of acquisition without heavy reliance on external marketing or paid advertising. This process works by establishing a viral loop. An existing user experiences value from the product and, either explicitly through sharing features or implicitly through the product's core functionality, introduces the product to new potential users. These new users then adopt the product, become active users themselves, and subsequently introduce it to others, repeating the loop. The product must make it simple and beneficial for users to invite or share. For example, a communication application like WhatsApp naturally encourages user-driven growth because to communicate with someone on the platform, that person also needs to be a user. This creates a strong incentive for existing users to invite their contacts. A key driver of this capability is often the network effect, where the value of a product or service increases for existing users as more people use it. When a product exhibits a strong network effect, users are directly incentivized to bring in others because it enhances their own experience. For instance, a social media platform becomes more useful to an individual user as more of their friends join because it expands their potential connections and content. The core capability, therefore, is to embed this mechanism into the product's design, making user acquisition a natural, almost automatic outcome of product usage.