Just ask the 241 Marines who were killed in their Beirut barracks by a truck bomb in 1983. No, I guess we can't.
Ask the Israelis who have been occupying the West Bank and the Gaza Strip on and off for years now, weathering regular suicide attacks.
Almost always, the occupiers underestimate the tenacity of the occupied.
"The Israelis have their Apache helicopters," one longtime friend of the Palestinians was saying with a shrug yesterday. "We have people who are willing to give their lives for the land. We just keep coming."
From his tone, you got the feeling this could go on for decades longer, maybe even for centuries, if it has to, regardless of the latest American president's latest roadmap for peace.
And if that isn't proof enough of the risks of long-term military occupation, now you can ask the young soldiers of the Army's 82nd Airborne Division.
They have lately been occupying Fallujah, Iraq, 30 miles west of Baghdad, a Sunni-dominated area that was once a ripe recruitment zone for Saddam Hussein's Republican Guard. Saddam loyalists can still be found in Fallujah, as can deeply religious Muslims who are eager to turn Iraq into an official Islamic God-state.
For the moment, Fallujah is just another part of U.S.-occupied Iraq.
Which means the old government is gone and a new one has yet to materialize. And this dicey interregnum is the messy responsibility of the Americans.
Which brings us to Monday night.
The way local witnesses tell the story, the trouble began at the end of evening prayers. The mullah urged his faithful - 200 at least - to walk together to a nearby school, which the occupying American soldiers were using as their barracks.
These soldiers, paratroopers from the 1st Battalion of the 325th Airborne Infantry Regiment of the 82nd Airborne Division, are trained splendidly for battle but hardly at all for occupation.
As the demonstrators neared the school, the American troops opened fire on them. That much is clear. Almost everything else - especially the why - remains a matter of sharp dispute.
"It was a peaceful demonstration," said the Sunni cleric Kamal Shaker Mahmoud. "They did not have any weapons. They were asking the Americans to leave the school so they could use it."
The BBC quoted one witness as saying that a man on a motorbike opened fire on the soldiers, leading to a massive counterattack.
For their part, the Americans insisted they fired only in self-defense, although various U.S. Army officials portrayed the precise threats in vastly different terms.
One officer, Lt. Christopher Hart, said that as the chanting demonstrators approached his men, two Iraqi gunmen with combat rifles appeared from behind the crowd and started firing toward the school.
"There was a lot of celebratory firing," another U.S. officer at the scene, Lt. Col. Eric Nantz, told Reuters, noting that Monday was Saddam Hussein's 66th birthday. "There were a lot of people who were armed and who were throwing rocks. How is a U.S. soldier to tell the difference between a rock and a grenade?"
By the time the story was weighed and polished by the U.S. Central Command, it wasn't just two Iraqis with guns or a few rocks that might have been grenades. Now 25 armed Iraqis fighters were firing at the U.S. troops.
The Americans "came upon a group of Iraqis that fired AK-47s at them and they returned fire," said the Central Command spokeswoman Yvonne Lukson.
Whatever the precise level of provocation, this much was clear: The American counterattack had been quite deadly to Iraqi civilians.
No American soldiers were killed or injured. The International Red Cross put the Iraqi death toll at 15. Ahmed Ghanim, director of Fallujah Hospital, said 13 Iraqi civilians were killed and at least 75 wounded. Some local witnesses had numbers even higher than that. The injuries included bullet and shrapnel and lost limbs. Doctors said all the injured were civilians. Some were children.
And all the bloodshed was duly beamed across Iraq and the rest of the Arab world by Al-Jazeera and other local media.
As were funerals for the various victims.
"Our soul and our blood we will sacrifice to you martyrs," hundreds of mourners chanted as they carried four simple wood coffins shoulder-high through the streets of Fallujah yesterday.
The sound of wailing echoed through the town's dusty streets.
It is a part of Fallujah's shared history now.
How the liberators became the occupiers, or so the story went. Thirteen dead civilians. Or was it 15? And when will the Americans leave?
And again, occupation was not as easy as it sounded.
Again, the occupiers were underestimating the tenacity of the occupied.