The idiom **措手不及** (cuòshǒu bùjí) is formed through a classical Chinese grammatical structure where "措手" (to place one's hands, meaning to deal with or handle) serves as the verb, and "不及" (not in time) acts as its complement, creating a resultative construction meaning "to handle, but not in time." It literally translates to "can't get one's hands arranged in time," vividly depicting a scenario of being caught so completely off guard that one has no chance to react or prepare. The phrase originates from military contexts in classical texts, describing a surprise attack, and has evolved into a common figurative expression for any situation of being unexpectedly overwhelmed or unprepared.