Funny how that was released yesterday, so it was already predicted.
How so? A problem that stops the work being finished in its predicted time plus margin can happen in the middle of a job. If it's bad enough there may be no way to recover the time. Even if it might be possible by abandoning the original work, having to repeat the possession later may be worse overall for
NR» and the ToCs, or even for passengers.
That doesn't really have anything to do with whether it's just one of things you only find out when you dig the hole, or is more "iatrogenic" - whatever the equivalent of that is (I'm sure the Greeks had a word for military, if not civil, engineers).