Do supermarkets know more about us than we do?

When you buy something at the supermarket, what makes you pick one brand - or one product - over another? Retailers invest huge sums trying to understand this decision-making process, or influence it, in a UK grocery market worth almost £200bn. We know supermarkets can learn a huge amount about us by studying what we buy. But our research also suggests that we form personal bonds with products over time, as we try to self-justify our buying decisions. In short, we do not just buy what we prefer, we end up preferring what we buy; and this means we are more open to influence than we might think.