The idiom "若无其事" is formed through a classical Chinese grammatical structure where "若" means "as if," "无" means "not have" or "there is no," and "其事" means "that matter" or "the affair." Literally, it reads "as if there is no such matter," constructing a vivid scenario of someone's demeanor. This phrase describes a person who behaves with complete composure and indifference, pretending as though nothing has happened or as if a significant event is of no concern, thereby capturing the essence of feigned nonchalance or calm unconcern in the face of a situation.