The idiom 彻头彻尾 (chè tóu chè wěi) is formed through a parallel and repetitive structural pattern common in classical Chinese, where the character 彻 (meaning "to penetrate" or "thorough") is repeated to frame and intensify the core nouns 头 (head) and 尾 (tail). This construction creates a vivid spatial metaphor meaning "from head to tail", which figuratively extends to signify "through and through" or "downright", thereby emphasizing an absolute, unqualified quality that permeates an entire subject from beginning to end.