It's an old Jewish joke,with, as always, a telling punchline: "You think it's easy being an optimist?"
The answer is in the question. As I spoke to the (still fairly) new Israeli ambassador the other day, I wondered if one of the qualifications for the job was to learn to accept that optimism was not just reasonable, but something that could be transmitted to other people, too. Mark Regev, for years the voice of Israel on our TV screens, is not one to put a gloss on problems. Time and again, during the 2014 Gaza conflict when things looked at their worst, he put Israel's case, admitting the mistakes as well setting out the reasons behind Israel's actions.
Rosh Hashanah, a time for reflection, gives him a chance to review where Israel stands in the 21st century. In short, he seems to find optimism not as difficult as one might imagine. Now, with antisemitism in Europe - to say nothing of Britain - at a higher level than for generations, he sees a number of silver linings behind the clouds. Such as, British Jewry is strong - even British students are prepared to listen to Israel's case. Such as, relations with some Arab neighbours have never been better. Such as, the UK government is as friendly to Israel as it could be. Both countries realise how important it is to maintain the best relations with each other.
Regev, Mr Israel for all those years in front of the cameras, sees a strong connection between that job and the one that has been his since first moving into the Kensington embassy six months ago. "In some ways, it is the same job. I am not a journalist. When I went on television and radio, I was acting as the government spokesman. That's what I do now."
Representing Israel comes with a double workload. Years ago, an Israeli ambassador, the late Yehuda Avner, came to a meeting of the Board of Deputies and declared: "This week I presented my credentials to the Queen. Today, I present them to the Jewish community." Other ambassadors have been quite sniffy about that relationship, as though it seemed to demean their diplomatic position. Ambassador Regev takes a central position. "I think it is right and proper that ambassadors of Israel work very closely with the Jewish community.
I want dialogue with Israel's critics. I want to engage.
"First of all, we are the Jewish country. Throughout the world, that is our ethos. I don't know how many Jewish events I have attended. I see that as an important part of my job."
And then comes the "but": "I would also say to the Jewish community that I have other responsibilities. An ambassador who would give all his time to the Jewish community, and the Jewish community alone, would be making a great mistake.
"My primary function has to be to work with the British government, and to make relations between the two countries stronger." It's a moment for reflection again. "When Prime Minister Netanyahu said his farewell words to me, it was clear to me that he expected me to be a powerful advocate of the Israeli case to the British people.
"My role is not just speaking to Israel's traditional friends. I want dialogue with its critics. I want to engage. I am confident that Israel's case is essentially just. There is no place which is no-go territory. I want to make the case for Israel across this country."
There is no doubt that he values the British Jewish community's own contribution to this. "I don't see that as a contradiction. The Jewish community in this country has contributed so much. It is a community that is not without influence."
Regev, now 56 years old, first arrived in Israel in 1982 from his native Australia, after a childhood steeped in Zionism and its youth movements. He was a leader in the local Habonim organisation. Now, he not only brings his profound Israel loyalties to London, but also those connections to Britain. "Having been brought up in Australia, part of the Commonwealth, many things here are very familiar. I'm also aware that things are very dynamic, changing.
"Since I arrived, Britain decided to leave the EU; a new prime minister has arrived. All very important for Britain, but not just for Britain, but for Britain's place in the world. l'm making every effort to bring Britain and Israel together. I find the attitude of government people here very positive; people who have visited Israel since Brexit. Their message is that they want to strengthen the ties between Israel and the United Kingdom."
What about antisemitism in Britain? The boycott movement? The Labour Party? "Of course, there are concerns. They are legitimate and I understand those concerns. I am working with the community on some of these issues. Very closely. As partners, we are acting much more than ever before. If Jewish students feel they are ill equipped to deal with [the issues they face] there is no doubt that things are going on on the campuses . I make a deliberate effort to go to the campuses to make sure that Israel's case is heard. Again, there is no no-go area. If you read the Hebrew press, you would think that all the students are running around [condemning Israel]. But I spoke to the Oxford Union. I had a very good hearing. Outside, a very small group were protesters. Inside, I got critical questions but I did not feel any hostility."
As for the Labour Party, "I have no doubt there is a certain milieu that is hostile. It's part of a parcel of issues. No doubt."
It's here that the diplomat becomes indistinguishable from the man on the television - the one who was never afraid to tell things as they are. "There some things [Israel doesn't] do so well. But some things we do very well. I think there is an understanding across the UK that the United Kingdom can do well with co-operation with Israel - like hi-tech, which we do spectacularly, especially cyber technology.
"We are all experiencing threats. These are all areas in which there is an understanding in Whitehall and Parliament. On the other hand, we can learn from Britain - in politeness, for instance. It would make Israel a better place. Not just for PR, but because we want Israel to be [that] better place back home."
More importantly, Israel and certain neighbouring countries have better relations than every before. And he doesn't restrict his comments to the two nations with which it has diplomatic relations - Jordan and Egypt. He won't name those other countries, but he says it is one of the "great untold stories". Saudi Arabia is often talked of as one of those places, but he won't even hint he is confirming that.
Perhaps another untold story is Israel's admiration for British Jewry, "There are things that the British community does that are better than any other community in the world. "My family in Australia was very involved with Jewish Welfare. Here is it Jewish Care. It is very well done. Something like the CST is an example to Jewish communities in other countries." The UJIA is "very important," he says. "I go to Jewish schools. Here, they excel in many areas. There are many things that British Jews can be proud of."
A lot of that will come to the fore next year with the Balfour Declaration centenary celebrations. It is all looking good - with exchange visits from top government personalities among many other things planned.
I have known 10 Israeli ambassadors - ranging from Michael Comay in his shirtsleeves during the Yom Kippur war, through the brilliant, erudite (and victim of an assassin ) Shlomo Argov, the heimishe Yehuda Avner, to the bright, funny Daniel Taub. Mark Regev, "Mr Israel" is set fair to rank with the best of them. After all, as he says: "I'm an optimist."