The phrase "乐不思蜀" is formed directly from a historical anecdote in which Liu Shan, the deposed ruler of the Shu state, declared he was too happy in his new captive life to miss his homeland; it structurally combines the four characters 乐 (happy), 不 (not), 思 (think of), and 蜀 (Shu, his former kingdom) to encapsulate that specific narrative into an idiom denoting becoming so pleasurably absorbed in a new environment that one abandons thoughts of returning to one's original duties or home.