Well stated. The statement is a deliberate oxymoron--it sounds contradictory on the service, but we can see through the literal meaning to the figurative meaning of "be prepared for anything that could go wrong".
If expecting the unexpected makes the unexpected the expected, we would have to expect what was once seen as expected to expect the unexpected. Thus, what was at first expected is yet again expected, making the unexpected the unexpected.
It reminds me of that brain teaser: A judge condemns a prisoner to hanging. The judge says that the man will be hung some day next week (Mon-Fri), but that the prisoner won't know the day, so that it will be an "unexpected" hanging. The prisoner says this makes no sense. He reasons that if he were not hung Mon-Thu, then he'd know it was on Friday, the last day, so he couldn't be hung on Friday. If Friday is out, then so is Thursday, Wednesday, Tuesday, and Monday following the same logic. So the prisoner concludes there won't be a hanging, since it can't possibly be unexpected. He returns to his cell in triumph. Then on Wednesday, the executioner shows up at his cell with a noose. It was quite unexpected