UK Independence Party (UKIP) leader Nigel Farage poses in front of a new campaign poster in Clacton-on-Sea, eastern England on June 21, 2016.

If you listen to marketing experts, the United Kingdom's decision to exit the European Union has one primary cause: The Brexit side ran a better advertising campaign, centered around citizens' love for their country.

"It was a very simple message that was very well repeated," said Ian Millner, co-founder and CEO of agency Iris Worldwide. "There was nothing rational about it. It was speaking to a heart and soul of a growing number of people in the U.K. that don't feel listened to."