Simpson helped curate the playlist to celebrate the UN 's International Day of Happiness . The song was written by American songwriter and producer Pharrell Williams, who also produced it with his brother Chad. Fans are encouraged to share the songs that make them happy .
Simpson helped curate the playlist to celebrate the UN 's International Day of Happiness . He will mark the day by performing at the SXSW festival . Fans are encouraged to share the songs that make them happy .