Oftentimes I've heard people who are not and have never been software engineers ask "When we want to built a bridge, engineers can tell how long it will take and how expensive it will be, how come with software engineers it's never the case?" (often implied: you software engineers have it easy, slackers! -- I believe we put this blame on ourselves with our immature culture, but that's another discussion)

What I usually answer to that is that, to begin with, that if they had actually dealed with big construction projects like bridges then they would not idealize those so much. And secondly, that this is not the right analogy. Bridge construction is a much stabler science, it had no "complexity explosion". A better analogy would be geophysical prospection : the theory it's based on is sound and mature but the unknowns dominate everything in predicting the outcome.