Having reported on Budgets for 30 years, I am wracking my brains whether I can ever remember such a rapid U-turn on the central element of any previous Budget.
And I really can't.
So what does it show?
Well partly the power of the Prime Minister, Theresa May - who was annoyed that the National Insurance (NI) rise was announced by the Chancellor with too little regard for the sensitivities of her MPs, and in particular with too cavalier an approach to the commitment in the 2015 manifesto not to raise NI.
It was Ms May's decision to dump the rise - or at least not to implement it this side of the 2020 general election.
Which of course leaves her Chancellor, Philip Hammond looking significantly weakened.
But it shows something else of note as well: that when a government is so overwhelmed by the burdens of exiting the EU and keeping Scotland in the UK, big accidents will happen.
For what it's worth - and as the respected Institute of Fiscal Studies has been tirelessly repeating - there was a strong intellectual case for increasing the NI rate for the self-employed, now that they are more inside the state's welfare safety net than they've ever been.
But when Theresa May has bigger fish to fry - in Europe, in Scotland - and she has a wafer-thin Commons majority, ditching political embarrassments pronto is far more important than a fiscally sensible and prudent reform.