Judging from the reactions, both in Israel and abroad, to this Sunday's bombing in Kana, something that should have been self-evident has been widely forgotten. So let me restate it: In war, mistakes are not merely possible, they are inevitable. They are an inseparable part of the price of going to war. And they do not make a justified war any less legitimate. Mistakes happen because wars, despite all the fancy hi-tech equipment, are still fought by human beings. And human beings are not infallible. "Precision" bombing, for instance, depends for its precision on accurate information about the target. And that information is usually obtained, analyzed and transmitted by human beings. By any reasonable standard Israel's intelligence agencies are outstanding. They manage, for instance, to obtain accurate advance information about an overwhelming majority of suicide bombing attempts, thereby enabling the security services to foil some 90 percent of all such attempts. No other country facing a similar campaign of suicide bombings has come close to matching this record. Nevertheless, "outstanding" is not the same as "perfect." Perfection is not an attainable standard in a business that depends on human beings. Agents can only pass on what they know and, being human, they do not know everything. Moreover, being human, they have no foolproof mechanism for differentiating fact from fiction - which means that even the best agents are sometimes fooled by the enemy's efforts at disinformation and concealment, and pass on false information in the belief that it is true. When possible, information is cross-checked against other sources. But sometimes there are no other sources. And sometimes the other sources have also been fooled. Therefore, mistakes happen. Buildings are identified as arms caches when, in fact, the arms are elsewhere. Trucks thought to be carrying weapons turn out to be carrying food. And buildings where civilians are sheltering from aerial bombardment in the basement are reported as being empty. By any reasonable standard, Israel's air force is also laudable. It has flown tens of thousands of missions, with a high rate of success. But for all the hi-tech gadgetry in a modern fighter jet, pilots also matter: That is why planes still have them. And pilots are human beings. They get tired; they suffer momentary lapses of concentration; they misunderstand orders. This is especially true when they are exhausted from flying thousands of sorties in just under three weeks, as has been the case in the current fighting in Lebanon. And so, they sometimes make mistakes. THE KANA bombing, whether due to flawed intelligence or pilot error, was a terrible mistake. Not only were there many civilians in the building, the building apparently had no connection with Hizbullah. But the fact that this particular mistake had tragic consequences does not mean there is something "wrong" with either our intelligence services or our air force, as many Israelis charged this week. Too many mistakes would indeed indicate a problem. But some number of mistakes, however tragic, is inevitable in any enterprise involving human beings. There has never been an error-free war in the history of the universe, and there never will be. If war is permissible only if it can be waged with zero errors, then this is the equivalent of saying that war is never permissible at all. Thus the idea that the Kana bombing somehow affects the justice of Israel's war on Hizbullah is ridiculous. If a war is justified at all, it is justified not on the assumption that there will be no mistakes, but because the goals of the war are sufficiently important to warrant the price of waging it - including the inevitable mistakes. Some of those mistakes, as has already happened several times in Lebanon, will kill our own soldiers, either through "friendly fire" or through accidents. And some will result in the unplanned and undesired deaths of enemy civilians. Incidentally, wars are also almost always disproportionate - because that is how they are won. If both sides simply exchange carefully calibrated tit-for-tat blows, a conflict can go on forever. Wars are won when one side applies enough force to make the other yield - which means that the loser usually (though not always) suffers greater casualties, greater destruction of physical infrastructure, and greater economic harm. Thus to say that a war must be "proportionate" is to say that it is forbidden ever to win - which, in turn, is a surefire recipe for prolonging the conflict ad infinitum. Given that mistakes and disproportionality are inevitable, is Israel nevertheless justified in fighting Hizbullah? If you believe that nations ever have the right to wage war in defense of their citizens, the answer is unquestionably yes. It is not just that Hizbullah started this war, launching a deadly cross-border raid with no provocation and no conceivable justification, given Israel's UN-certified withdrawal from every last inch of Lebanese land six years earlier. Hizbullah is also unabashedly dedicated to Israel's destruction. It is armed and financed by the Iranians, who openly call for Israel's eradication. And in the six years since Israel withdrew from Lebanon, it has built up a network of border fortifications, sophisticated command and control centers and a huge arsenal, including 12,000 to 14,000 rockets, all for the exclusive purpose of being used against Israel. As Hizbullah leader Hassan Nasrallah openly told a news conference on July 12, his organization started preparing for war against Israel from the moment Israel quit Lebanon. These days, of course, many "enlightened" Westerners argue that war is never justified. If a country is attacked, they believe, it must either refrain from responding altogether, or confine its response to an attack of equal magnitude, leaving the enemy's offensive capabilities unimpaired. Then it must meekly await the next attack. But anyone who believes that countries have a right and duty to protect their citizens must learn to live with the following truths: Eliminating a threat usually requires a "disproportionate" response. And the execution will never be error-free.