Why We Sing "Auld Lang Syne" on New Year's Eve

On New Year’s Eve in 1929 Guy Lombardo and the Royal Canadian Band took the stage at the Roosevelt Hotel in New York City. At midnight, as a transition between radio broadcasts, the song they chose to play was an old Scottish folk song Lombardo had first heard from Scottish immigrants in Ontario. The song was Auld Lang Syne.
It must have been a hit because  after that the band played the song every December 31 until 1976. Lombardo, who died in 1977, became known as "Mr. New Year's Eve".