As the Israeli raids on Gaza and Palestinian rocket attacks on southern Israel continue, BBC Middle East editor Jeremy Bowen assesses why both Israel and Hamas seem likely to pursue the conflict.
After two weeks of war both sides have reasons to believe they can fight on.
Israel has suffered relatively light casualties, a fraction of the dead and wounded of Gaza. Even though many reserve units have now been mobilised, which means a large number of husbands and fathers are in uniform and potentially in the line of fire, public support for the war is holding steady.
The government has managed the war of Israeli expectations far more effectively than it did in Lebanon in 2006. Victory has been defined in less sweeping terms, so that it will be harder for anyone to accuse the government of failure.
Israel has not won the arguments internationally over its methods
Even so, it has set objectives that need to be met if Foreign Minister Tzipi Livni and Defence Minister Ehud Barak are going to have any kind of political career when this is over.
Unlike Prime Minister Ehud Olmert, who is leaving office because of allegations of corruption, Mr Barak and Ms Livni face a general election on 10 February.
They have set two main objectives, neither of which has been achieved yet.
First, damage the Hamas military wing so badly that they will either be unable to launch rockets into Israel, or be so intimidated that they will not dare.
Israel's second demand is that the border between Gaza and Egypt is controlled so that Hamas will not be able to bring in weapons and money through tunnels.
The conflict has lasted the best part of a century, which suggests that this latest episode, bloody and brutal though it is, will not be decisive
Israel can feel the international pressure to stop. It has persuaded many of its allies that it has the right to defend itself, but it has not won the argument over the methods it is using. Israel's international image is taking a severe beating because it is killing so many civilians and so many children.
But with the United States abstaining in the ceasefire vote at the UN Security Council, Israel feels comfortable enough to dismiss the resolution because it says it is "not practical and will not be implemented by the Palestinian terror organisations".
Moment to fight
Hamas has reasons to fight on too. Like Israel, it has dismissed the ceasefire resolution. It has demanded a ceasefire that opens all Gaza's crossings to Egypt as well as Israel, and a halt to military action and complete pullout by the Israelis.
While it can fire rockets into Israel and mortars and rifles at Israeli troops, Hamas will not consider itself beaten.
Israel's aim is to stop Hamas rocket fire completely
Hamas leaders in Gaza have gone underground. But based on the few messages that they have sent out from their hiding places, and statements from Hamas leaders in exile, it is possible to make some reasonable guesses about their thinking. They have an ideology of struggle, resistance and sacrifice. They could have extended the ceasefire with Israel but chose not to do so.
Hamas believed they would have to fight Israel at some time (the feeling was mutual) and it seems that they have decided that the moment has come.
Civilian deaths in Gaza are most likely seen not as reasons to stop but as a reason to go on. I can't say for sure, but if I was able to sit with Hamas leaders, as I have done quite a bit in the last year, I think this is how their logic would go.
They might say that Israel has shown its real agenda towards Palestinians - not peace, but war and death. And they might go on to say that stopping now would betray the dead and encourage Israel to go in even harder.
The template of the 2006 war between Israel and the Lebanese group Hezbollah is in the minds of both sides.
Hamas would like to do the same as Hezbollah, and take on the most powerful army in the Middle East, punish it, and live to tell the tale.
Hamas is intent on surviving its clash with the powerful Israeli army
That is an experience Israel does not want to repeat. It wants its enemies to be nervous, very nervous, about what it might do.
If Israel is going to fight on, the next stage will be for it to deploy the reservists who have been mobilised and equipped in the last 10 days or so be sent into Gaza.
Committing the reserves means the operation moves into a third phase, seizing more ground in Gaza, following the first week of air strikes, and the ground offensive of the second week.
The war in Gaza is the latest instalment in a very long conflict. Foreign leaders and diplomats who are trying to create peace between the Palestinians and the Israelis should take a long perspective. After all, the Palestinians and the Israelis do.
The conflict has lasted the best part of a century, which suggests that this latest episode, bloody and brutal though it is, will not be decisive.