"Everybody has a plan until they get punched in the face." Mike Tyson's infamous warning for his opponents could easily apply to the new occupant of Number 10.
Giving his first speech outside Downing Street, the new prime minister hinted at what his priorities will be – from easing the cost-of-living crisis to keeping commitments on defence spending.
But what happens when those plans make contact with reality? Can Mr Burnham's "Manchesterism" work on a national level? And will international events interfere with his domestic agenda?
Niall Paterson is joined by Sky's chief political correspondent Jon Craig to assess what might happen in his first few weeks and months in office.
Have you got a question for Niall? Email us: why@sky.uk