Pharrell Williams' 'Happy' was the best-selling song of 2014, but it was originally written for another artist. Pharrell offered the song to CeeLo Green, who recorded a version of it that his label ultimately decided not to release. Pharrell then recorded it himself for the 'Despicable Me 2' soundtrack. The song was a 'sleeper hit,' taking months to gain traction before becoming a global phenomenon. Its success was supercharged by the release of the world's first '24-hour music video,' a website that played the song on a loop with hundreds of people dancing across Los Angeles. The song reached number one in 24 countries and won two Grammy Awards. Pharrell revealed that he wrote nine different songs for the movie before finally coming up with the melody for 'Happy,' proving that persistence is often the key to creating a career-defining hit.