I think a significant issue in software is the comparatively unconstrained input space. I would imagine the average natural gas power plant would have more tha

I think a significant issue in software is the comparatively unconstrained input space. I would imagine the average natural gas power plant would have more than a few issues if you fed it pure hydrogen instead of whatever methane based mixture it was designed for. Similarly I imagine there are other inputs that have tight specification, lubricants, etc. But, these inputs are relatively easy to control via both human and machine processes and there aren't that many combinations you would consider valid. There are complex inputs in the physical world, for example the impact of complex wind patterns on bridges, but I still feel this is simpler than many input spaces in software. In software, at some level you're almost always dealing with human or machine generated input which may be very complex in nature such that that even after all reasonable efforts at validation the size of the possible input space is massive if not effectively infinite. We're getting a bit better at dealing with this, e.g. fuzzing, but there is a long way to go for fuzzing to be viable on more complicated inputs.