Berger's fourth principle is Public visibility. The idea is simple: people imitate what they can observe. If a behaviour or product is visible, others notice it and are more likely to adopt it. If it is private, adoption depends entirely on direct communication rather than passive observation. Designing products and behaviours to be more observable increases natural spread. Apple's white earphone cables were famously distinctive when most competitors used black ones: every person using an iPod was a visible advertisement for the product. The Lance Armstrong charity wristbands made the wearer's donation visible, which spread the behaviour. Making the private public is a simple but powerful design principle. The fifth principle is Practical Value. People share useful things because sharing useful information is a form of generosity: it helps others. Content that gives people something valuable, a money-saving tip, a useful skill, an important warning, tends to spread because sharing it allows the sharer to help someone they care about. Berger found that genuinely useful content, particularly content that saves people significant money or time, tends to spread even without other STEPPS elements. The desire to help people we care about is a powerful and reliable driver of sharing.