Because when David Cameron or Tony Blair took leadership of their respective parties, their overall mission was clear. Both were unashamed modernisers of organisations that had been out of power for some time. Both had a mandate to shift their party towards the centre ground.
However, the first thing Miliband needs to do is throw off the suspicion that he was a 'compromise choice'. His inauguration has not inspired the sort of awe that accompanied Cameron's or Blair's and his first comms challenge is to be taken seriously by the media. The right-wing newspapers (let's face it, most of them) are never going to love Ed, but he has to move beyond being a joke; even strike some fear into Fleet Street.
His second challenge is to communicate a clear vision of where he is taking Labour. He cannot afford to appeal to everyone - as he did with Andrew Marr on Sunday morning - for too long. Like any 'brand', he needs both personality and promise; an underlying truth behind his mission.
This vision must transcend narrow constituencies. He made the first step by insisting on Sunday he was 'nobody's man'. But if he is ultimately perceived as being 'in the pocket' of the trades unions or public sector workers, he will fail. Because, as every incumbent has discovered in recent times, one must win over 'middle England'.
Miliband is not yet photogenic and lacks media nous. He will be hamstrung by currently lacking a constituency of support in the media. All of this because he has suddenly come out of the leftfield.
But this could also work to his advantage. Unlike his brother David, Ed is so far an unknown quantity. He has a clean slate on which to paint his brand.
At 41, he is young enough to learn, to make the odd mistake, but still to get it right.
And most importantly, the leadership election suggested he could be made of the right stuff. He certainly used enough charm and strategic prowess to win. Moreover, he demonstrated the sort of ruthlessness that leads to the top.
It looks unlikely now, but this could be the sort of comms campaign that rewrites history.