The idiom "破釜沉舟" is formed by concatenating two parallel verb-object phrases: "破釜" (break the cauldrons) and "沉舟" (sink the boats). Each character denotes a concrete action or object, "破" (to break), "釜" (cauldron), "沉" (to sink), and "舟" (boat), and their combination creates a literal sequence of destructive acts that together convey a single, unified meaning of eliminating means of retreat to express unwavering resolve.