​​Sports shoe brand Nike benefits hugely from having its 'swoosh’ logo prominent on all its shoes. I spent several days on the streets of London and its underground system trying to estimate how many times an average commuter would see the Nike logo in a year. It’s probably over 200,000. These exposures have a very small impact on brand choice, but they add up. We are a social species. If lots of other people choose a particular brand, we tend to think it must be a good choice due to a powerful psychological phenomenon known as 'Social Proof’.