I think the bridge analogy can work a different, equally effective way: we can build software based on well-established and tested engineering principles, with tools and materials that have a known, verifiable set of behaviors.

I'm not a materials/mechanical engineer, but it seems that engineers can build bridges properly the first time (most of the time, right?) because they are working against a set of well understood, well tested physical laws (for lack of a better word). Even I write the perfect, say, shopping cart application, that bit of software still relies on programming frameworks, web servers, operating systems, and hardware systems that have known issues.