Reciprocity is the idea that we’re much more open to engage with people and brands after they’ve provided us with real value. A classic example is the way charities include pens in their postal mail-out appeals. The facts the pens are low quality and we already have lots of pens are overwhelmed by the feeling that the charity – perceived as a needy organisation – has given us something. We need to give something back. This kind of thinking also works in the world of virtual goods, which is why companies such as SessionM are finding success.