In DDads work he was an engineer and early on in his career he was designing a piece of equipment that would fit onto another piece of equipment and cost about a million quid.
It was produced, sent to site, and they got a message back that it didn't fit. He'd designed it the wrong way round.
He spent a week thinking, that's it, my careers over, and eventually went into the heads office to confess. The head just turned to him and said oh don't worry, we sent it somewhere else.