The idiom "乐此不疲" is formed by directly combining four characters: 乐 (lè, meaning "to enjoy"), 此 (cǐ, meaning "this"), 不 (bù, meaning "not"), and 疲 (pí, meaning "tired"). These characters are arranged in a literal sequence to convey "enjoy this, not tired", creating a phrase where the act of enjoying something results in an absence of weariness. Its structure arises from classical Chinese syntax, used to express persistent engagement without fatigue.