The formation of "一模一样" is a vivid, conceptual construction based on metaphorical imagery and emphatic repetition. It directly translates as "one mold, one sample", visually stacking two nearly synonymous phrases, the first ("一模") referring to an object cast from a single mold, and the second ("一样") referring to a single standard or pattern, to create a powerful, rhythmic emphasis on perfect, indistinguishable sameness, as if two things are duplicates produced from identical origins.