乐不思蜀 (lè bù sī Shǔ): indulge in pleasure and forget home and duty

乐lè不bù思sī蜀Shǔ

indulge in pleasure and forget home and duty

A captive king enjoyed his comfortable exile so much that he said he never thought of home. For someone so pleased with where they landed that they have forgotten what they came to do.