That's exactly my conclusion, every time I've had an issue it's been the "unknown unknowns" that have caught me out.  Our borehole saga is the classic, well over a year trying to find the cause of the problem based on assumptions that the spec we'd been given (and paid for) was accurate, only to find in the end that the hole had been drilled 17m short and the supposed problem of the bottom of it being full of packed sand that I'd been trying to solve for over a year didn't exist. Added well
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