What unites Cameron and Clegg
That is what distinguishes those politicians who shape events from those who end up shaped by them.
It was vast reserves of nerve which allowed both David Cameron and Nick Clegg to run for, and win, their parties' leadership against far more experienced opponents; which allowed them to take on their parties and challenge some of their long-held assumptions and which yesterday led them to take a huge jump into the political dark.
It was - as Danny Finkelstein has written in The Times - a far bigger call for them than Tony Blair's much hyped decision to scrap Clause Four.
In the early hours of election day I sat at the back of David Cameron's campaign bus with the Tory leader as he began a long night of campaigning. The polls and the pundits were predicting a hung Parliament but he'd been told by his campaign team that he would get a majority and appeared to believe them.
Twenty-four hours later came the early signs that that prediction was wrong. Twenty-four hours after that, despite exhaustion, disappointment and confusion about the way ahead, the Tory leader made a decision to go for broke - offering the Liberal Democrats a full-blown coalition and ignoring most in his party who were calling on him to govern as a minority. Many thought that he was just going through the motions; even his close allies, and perhaps Mr Cameron himself, thought the Lib Dems would not have the stomach to take up his offer.
In that election week I also had the chance to chat at length to Nick Clegg. Though he was a sceptic about so-called Clegg-mania and fearful of the classic pre-polling day two-party squeeze he clearly believed that the only way for him and his party was up.
When he too faced the grinding disappointment of losing not gaining seats he had the clear-headedness to focus on the opportunity which presented itself. And also to ignore the cries of betrayal of those who'd assumed that he'd not meant what he said when, prior to the election, he said that the party with most seats and/or votes would have a mandate to seek to govern.
The result of Cameron and Clegg's nerve is a deal that still has many scratching their heads or angrily denouncing them.
What they ignore is what unites them. They are both bright, confident public-school-educated young men who are surrounded by others like them.
Cameron is the first socially liberal Tory leader in a long time and Clegg the first economically liberal leader of the Lib Dems. Though there is much that divides them there is a great deal on which they agree. Both regard parts of their own party with disdain.
There is one last thing that our new prime minister and his deputy share - a desire for power.