The engineer who built these towers proved to be mentally unsound and the towers structurally unsound, so Brunel was brought in to rebuild them (which might happen again). The story goes that he was at first most reluctant to pass judgement on the work of another engineer, however bonkers. Gentlemen didn't do that to one another.
This was in 1855, when engineering as a profession was young and about twenty years before the Tay Bridge disaster firmly fixed in people's heads the idea that one engineer won't do. Much as even accountancy firms themselves have to get an accountant in to audit their books, on a big enough job engineering firms get one another in to check they've got their sums right. This the work of Consulting Engineers.
In the IT world we bandy the word "consultant" around with a certain amount of levity. In the US a consultant doesn't really seem much different from what in the UK we call a contractor: in everything but name a temporary employee. In the UK there is a slight difference, which a contractor once expressed to me (a consultant) in this way: contractors don't have to write reports.
More generally contractors build the system they way they are told to, consultants have an opinion about how the system should be built. This distinction is not lost on the tax authorities.
Anyway, what with all this talk of "craftsmanship" there's been about the place recently thoughts naturally turns towards the more mature disciplines. A significant aspect of those, in many cases, is that it's awfully hard to get certified to practice.
That's in part so that individuals can bear some liability if the job goes tits-up because the certifying bodies certainly will. This is as imperfect as any human institution, but at least they try. Another aspect of this is genuine consultancy. If you, you personally, are going to bear liability for it all going pear-shaped then maybe you sould spread some of the
blame load by getting someone else in.
Notice that in the medical field, if you aren't sure of a diagnosis then you can ask for a second opinion. If your doctor isn't sure, they'll go and get one by themselves.
This seems not to happen much in the IT field. Perhaps another symptom of our immaturity? When was the last time you worked on a project where the prime contractor brought in a competitor to check that they'd "got their sums right"?
Have we had our Tay Bridge yet? Maybe. In some domains, avionics, for instance, you do hear of multiple independent implementations. That's not quite what I mean, though.
Why don't IT companies running projects (of a certain size or complexity) routinely get the competition in to express an opinion? Why don't clients demand this as part of their risk mitigation strategy? What is it going to take for folks to bring a genuinely professional standard of conduct to IT?
Update: it's two days later and no-one has thrown down the gauntlet. I was expecting some bright individual to come back at me with a "you work for a consultancy, so you tell us why this doesn't happen" But no-one seems to be biting....