We all make mistakes, of course.
But I'd have thought Osborne might have a) double checked this and b) had the grace not to blame his assistants when it's been shown he was wrong.
And this really does smack of incompetence. As the Lib Dem, Steve Webb, showed on 6 October, the plan made no sense, and he reasoned that just by applying some common sense logic to the numbers.
Which says to me that Osborne lacks the ability to apply that common sense logic to numbers. Which is very worrying for someone who wants to be chancellor.