I think it's attributed to "luck" because the Romans didn't have the theory or the tools necessary to do a systematic search of the problem space and didn't und

I think it's attributed to "luck" because the Romans didn't have the theory or the tools necessary to do a systematic search of the problem space and didn't understand why one way of doing it is better than another. It's similar to ancient metallurgy, where we know that some quite impressive results were produced sometimes, but the artificers themselves didn't know exactly why their product was better than the product two countries over.