Even on the day that George Osborne wants to sound tough, demanding that the rest of the EU rejects closer and closer political union - and gives legal guarantees to the UK that our businesses will never suffer because they are not in the eurozone, it is almost impossible, observing the chancellor here, to imagine that one day he might stand on a platform and call for the UK to leave.
He is positive about the chances of a deal, and doesn't want to countenance the idea that the negotiations might not achieve very much.
There have been nerves in government that the Eurosceptic side of this argument is gaining momentum.
Ministers' official position, indeed a bargaining chip in the negotiations, is that hypothetically, if other countries don't sign up to our demands, they are ready to campaign to go.
But, observing Mr Osborne in Berlin, continental Europe's most powerful capital, cracking jokes about British and German sausages, clearly delighting in his political friendship with the German finance minister, Wolfgang Schauble, it is Mr Osborne, the self-professed optimist, who is not just an advocate of the UK"s emerging negotiating strategy but of the benefits of our membership itself.
He is visibly confident, but this will be difficult.
He confirmed the changes the government wants to make will require a new EU Treaty.
There is zero chance of that happening before the British vote, and ministers can't answer how or when it might happen.
And for the Chancellor's demands on legal protections for business and the City of London today, it's not clear why other countries will sign up to give equal consideration to Britain's interests, as well as their own - two new challenges on the list, in addition to restricting benefits' migrants, changing the principle of freedom of movement, and getting some powers back for our Parliament.
For Mr Osborne, who twice today refused to rule out becoming the next Conservative leader, his political future depends on steering the government through this vote, which must happen by the end of 2017.
He may well be an optimist, but on this, he needs to be right.
"I'm an optimist".