1,000 to 1: why did Israel agree to the swap?
I have a proposition for you this week: I'll give you one pound if you promise to give me £1,000 in return.
No? So why do you think Israel has agreed to release 1,000 Palestinian prisoners in return for the release by the Palestinian Islamist group Hamas of just one captured Israeli soldier?
The 25-year-old soldier's name is Gilad Shalit, and he's probably one of the best known men in Israel. He was snatched by Hamas fighters more than five years ago close to the border between Israel and the Gaza Strip - and he's been held, incommunicado, somewhere in Gaza ever since.
Within the coming days, he'll be freed, and there'll be mighty celebrations across the length and breadth of Israel.
His family, who have waged a relentless campaign to keep his name in the public eye and to put pressure on successive Israeli governments, will be ecstatic.
So will 1,000 Palestinian families, especially the relatives of the 315 Palestinians who were serving life terms in Israeli jails. (There are thought to be in total more than 10,000 Palestinians in Israeli prisons.)
But why did Israel agree to the lop-sided deal? There are several reasons: first, because it is an Israeli tradition to bring every lost soldier home, dead or alive. In the past, similar deals have been done to win the return of slain soldiers' bodies, or even of body parts.
Israel is a small country, with a conscript army. Israelis accept the reality of combat risk in the knowledge that the State will do anything, if the worst happens, to "bring the boys home".
Second, because Israel's prime minister, Benjamin Netanyahu, needed a victory. He's lost two important regional allies - Egypt's President Mubarak and Turkey under its ever-more assertive prime minister Recep Tayyip Erdogan - and was unable to prevent the Palestinian leader Mahmoud Abbas scoring a substantial propaganda coup at the United Nations last month with his appeal for Palestine to be recognised as a full State member of the UN.
So the deal for the release of Gilad Shalit is, in the words of Israeli political commentator Yossi Verter of Haaretz, "the most important deal of his [Netanyahu's] life ... he will forever be remembered as the man who brought back Gilad Shalit."
But the truth is that this deal has been on the table, more or less in its current form, for quite a while. What's changed is the regional political environment.
As Mr Netanyahu himself candidly put it: "With everything that is happening in Egypt and the region, I don't know if the future would have allowed us to get a better deal -- or any deal at all for that matter ... This is a window of opportunity that might have been missed."
As for Hamas, it needed to do something to show, after Mr Abbas's coup de théâtre at the UN, that it's still in the game. A thousand celebrating Palestinian families means thousands more Hamas supporters. The message is a simple one: Hamas's armed struggle gets 1,000 prisoners released, whereas the endless non-negotiations of Mr Abbas's Fatah get nothing.
Each side made some concessions to get this deal signed. Israel agreed that some, although not all, of the released Palestinian prisoners will be allowed to live in the West Bank or Gaza Strip (there was, apparently, endless haggling over individual names); Hamas agreed that some of the best-known prisoners, including the charismatic Marwan Barghouti, much touted as a potential future Palestinian leader, will stay behind bars.
As for what follows, who can tell? With both Netanyahu and Hamas strengthened, and with a shaky Gaza ceasefire in effect yet again, might they now be able to move forward on more substantive issues?
Optimists say it's possible. But in my experience, when it comes to the Middle East, optimists are usually disappointed.