Twelve Israelis killed was the final toll of Thursday’s terror attacks in Sinai, which took the lives of a similar number of Egyptians and tourists from elsewhere. Although this is less than the number of those killed in a bus bombing in Beersheba a month-and-a-half ago, the Sinai story has far outplayed the Beersheba bombing in the Israeli press, which have devoted enormous time and space to it.

Why Sinai more than Beersheba?

The Sinai Peninsula has long been for Israelis, both between 1967 and 1981 when it was under Israeli control and after its return to Egypt, an inexpensive Shangri-la. For decades now, hundreds of thousands have flocked every year to its stunning beaches and coral reefs with their backdrop of dramatic peaks and its temperate sea that is hardly colder in January than in July. For those with upscale tastes, Sinai offered comfortable and luxury hotels for a third of their price in Israel or in Europe. For the less demanding, it was dotted with small bungalow colonies where a thatch-roofed hut could be had for a pittance.

Sinai was for many Israelis, particularly the young, the perfect getaway: close-by, a mere five-hour bus ride from Tel Aviv, yet infinitely removed from the hassles and tensions of life in Israel. For a few hundred dollars, you could have a week’s vacation full of water, sand, sun, and stars, with more camels than cars on the horizon.

Never mind that the Egyptian officials at the border crossing at Taba were cold and that you always crossed with the aching knowledge that all this once had been yours and might have remained so if the 1977-79 Israeli-Egyptian peace negotiations had been conducted more wisely. The Bedouin along the coast, who didn’t much like the Egyptians, made up for it with their friendliness, and what difference did it make whose flag flew over the sands?

But it turns out to make a very big difference. Shangri-la has been blown sky-high and it will be a long time before Israelis flock back to it. This is not so much because 12 of them were killed there – no one in Israel has stopped going to Beersheba – as because of the fact that the nightmare of the dozens of wounded and the thousands of unscathed only began when the bombs went off.

What followed were hours of Egyptian incompetence and bureaucratic impediments that were expressed in the absence of rescue teams, in no or insufficient medical care, and in tormentingly long waits at the border, where officials at first refused to let casualties be transferred to hospitals in Israel without their passports – which in most cases were lost in the blasts.

This would not have happened in Beersheba. It sometimes matters whose flag flies where – especially if the flag that isn’t yours belongs to a country in which you aren’t well liked and with a culture and ways of doing things that are different from your own. Which is why the ache never really goes away and will remain even after Israelis begin returning, one day, to Sinai.

The 1977-79 Israeli-Egyptian peace negotiations, generally held up as a model for the amicable settling of disputes between old enemies, were badly bungled by Israel in two respects: the giving up of too much territory – and of not enough of it. The not enough was the Gaza Strip, which the government of Menachem Begin should have insisted on returning to Egypt. The too much was the Sinai coast south of Eilat, which it should have insisted on retaining at least part of.

But didn’t the Egyptians themselves, one may fairly ask, insist in those negotiations on a total return to the 1967 borders, which meant getting all of Sinai and leaving Israel with Gaza? The answer, of course, is yes – but that is precisely where the bungling occurred. Had Israel, instead of taking foolishly maximalist positions early on in the negotiations – in which it demanded a large chunk of Sinai – and then retreating from them entirely because of furious Egyptian opposition, quietly asked in advance for minor territorial adjustments, it would in all likelihood have gotten them. This might have included Egypt’s trading a sliver of the Sinai coast for a roughly equal amount of land that would have eliminated a saw-tooth between Sinai and the Israeli Negev in Egypt’s favor. If the return of all of Sinai had depended on this, it is hard to see how President Sadat could have refused.

Although this may all seem like spilled milk now, it continues to have its sour aftereffects – particularly in Israel’s stalled negotiations with Syria over the Golan Heights, in which the Syrians have felt honor-bound to follow Egypt’s precedent and not cede an inch of territory either, lest they appear to be weaker than their Egyptian rivals. The Begin government should have realized in 1979 that what Israel could not get from Egypt, it would also never get from Syria.

Flags matter. Israel listened in 1979 to those who argued that in times of peace it was all the same whether Israelis visited a Sinai coast belonging to Egypt or Israel. It should learn its lesson and not to listen to the same argument now about the Golan Heights or parts of the West Bank. You have no control over what isn’t yours. That is why it is crucial to decide in advance, without leaving it to the vagaries of negotiations, what must be yours and what needn’t be.

Mr. Halkin is a contributing editor of The New York Sun.