But if the price of dispossession is further dispossession, who is to blame?
Mr Gross blames Hitler for the evil that befell his family. Mr Shibl blames the Israelis for leaving him without a home or a country. Yasser Arafat and Yitzhak Rabin, who meet in Cairo today in an attempt to preserve their peace accord, might learn something from the lives of Mr Gross and Mr Shibl; they might come to understand the intractability of history and the need for settlements rather than solutions.
My journey from Beirut to Trzebinia, and eventually to the site of the Treblinka Nazi extermination camp, started as a routine reporter's search in Israel for the home that Yussef Shibl, then a 14-year old Arab schoolboy, fled under shellfire in 1948. Today, he is an economics professor at the American University of Beirut, and he told me his story of exile amid a sad bundle of old family snapshots and valid, but now worthless, land deeds.
Like the other 3.5 million Palestinian refugees who left - or whose parents or grandparents left - their homes in what was about to become Israel in 1948, he cannot return. 'My father Ahmed built our home in 1936 - he had it designed by a Lebanese man - and we planted trees in the front garden,' Mr Shibl said, fumbling for a badly stained photograph of a small boy riding a bicycle behind the house. 'There were six rooms. There was a fine iron gate between the garden and the road. I was a pupil at the Sixth Elementary School in Acre, a very good school. My father was acting director of the local forestry department under the British Mandate.'
In November 1947, the United Nations confirmed the partition of Palestine into two states, one Jewish, one Arab; Acre lay in what was to become Israel. Mr Shibl remembers the sound of shooting around the town after a Jewish convoy was ambushed on the road to Nahariya. 'My father decided that I should leave; he thought we should travel to Lebanon for a few days - weeks at the most - until the fighting died down, then return to our home.
'On the day before leaving, I went to my school to say goodbye to my friends and teachers, and to return the library books I had been reading . . . We left our furniture. We just picked up our clothes, and left for Lebanon. We travelled in our family car, a new Plymouth my father had just bought. There were six of us, my father and brother, my two sisters and a friend.'
Mr Shibl sketched a map of his home for me, complete with crossroads and a local bank. It proved accurate enough. There was his house behind a screen of trees, the delicate iron gate to the road just as Yussef Shibl left it 45 years ago. Only, of course, the occupants of the house were now Israelis.
Tsvi Gur opened the door. He is a butcher, who served in the Israeli army in occupied Lebanon, ironically not far from where Mr Shibl lives. Who was Shibl, he wanted to know? I told him the story, and Mr Gur went to fetch his elderly father.
Tsvi Gross (his son Hebraicised his name when he joined the army) moved into the house in 1950, two years after the Shibls left. 'It was a lovely house - I never knew who lived here before,' he said. 'Why did this man Shibl leave? Was he threatened? What reasons did he give you?'
I repeated the story of Yussef Shibl.
'And I was driven from my home,' Mr Gross said. 'I was born in Poland. The Nazis killed all my family. I am the only survivor.' The old man handed me a series of snapshots every bit as dated, and infinitely more tragic, than the pictures Mr Shibl had shown me.
'The Germans came to our town of Trzebinia in 1939. They broke the door and pushed their way into the house. 'Out, out,' they shouted. I was hiding in the double bed, curled up under the blanket. They used their bayonets in the bed.' Mr Gross clenched his fists, one above the other, and jabbed downwards.
'The Germans took my father. They took everyone in the house to the market. They took my father to a labour camp as he was a healthy man. In 1944, everybody (there) got typhus. He was one of the last to die. They took my brother to a camp. He died there. I don't know what year, but he never came back.'
Mr Gross handed me a photograph of a dark-haired woman with large, haunted eyes. 'Mother went to a concentration camp, and straight to the crematorium. The gas chamber. I know nothing more. That was in Treblinka; 1943 was the year it happened.'
I wondered if Mr Gross, after all these years and dark memories, could trace those old streets of Trzebinia? He was uncertain. But I helped him to draw a rough map with a square he referred to as 'Rinek' and the street where he lived. His father, like his grandson today, was a butcher, but there was no one left who would remember what happend to his town and its Jewish population.
Or was there? I drove into Trzebinia on a cold, windswept day with Mr Gross's map in my pocket. There was Rynek, the town marketplace. And there was the street in which the Gross family had lived, still lined by the dilapidated houses from which the Jewish families were dragged by the Nazis 54 years ago. The ground floor of the Gross house was derelict, the upper floor lived in by Poles, who refused to talk to me, at one point demanding 50 Deutschmarks merely for the privilege of taking pictures of the broken front door.
Then an old, unshaven man stuck his head out of a neighbouring window. 'I think I remember the Gross family,' he said. 'They were butchers. So the boy got away, did he? Yes, the Germans went through the house with bayonets.' The old man jabbed his clenched fists up and down in the same way that Mr Gross had done. 'Memories fade,' he said.
Or do they? I drove down to the old Jewish cemetery where some of Trzebinia's murdered Jews lie buried. Not long ago, a group of Poles proved that, even in death, these Jews have their enemies. I found many Jewish gravestones newly uprooted, broken in half, their Hebrew inscriptions hacked off.
This was no place for Mr Gross to return to, even if he were minded to. Yet it seemed important to make one last journey, northwards across Poland to an overgrown railway station called Treblinka, a place of rusting tracks and a gentle forest where no birds sing, where - in the death camp the Germans themselves destroyed in 1943 - Mr Gross's mother was sent to the gas chamber.
I handed the snapshot of Mrs Gross to the Polish camp guide. Of course, it was useless. 'There are no documents,' he said. 'The Germans destroyed all the files.'
A few yards away, the wind had uprooted a tree, and the guide bent down on one knee beside it. 'This is where the crematorium was. All the ashes are beneath here.' He picked up a small piece of bone, part of a skull and a single, artificial denture that had been unearthed by the tree's roots. 'When the Israelis find these,' he said, 'they take great care of them, and take them back to Israel.'
It is a terrible, uncompromising end to a story of dispossession. The men who murdered Mr Gross's family and drove him from the country of his birth, were indirectly responsible for the exile of Mr Shibl. Certainly, Mr Gross has suffered far more dreadfully than the Palestinian whose home he lives in. But they are men of equal innocence, their fates equally undeserved.
Mr Arafat's agreement with Mr Rabin takes no account of the 1948 Palestinian refugees such as Mr Shibl; under the PLO's accord, he cannot return to his home. But Mr Shibl does not understand why a man from Poland should live in his family home. The Gross family want to keep what they regard - legally under Israeli law - as their home. And a visit to Trzebinia proves that they cannot 'return to the land they came from' - as Mr Arafat's Palestinian opponents insist all Israeli immigrants should do.
That, ultimately, is what Israelis and Palestinians have been fighting about these past 45 years - and what Mr Arafat and Mr Rabin will ultimately have to resolve.
The story of Yussef Shibl and Tsvi Gross can be seen on Channel 4 this Tuesday at 9pm in 'The Road to Palestine', the second part of the series 'From Beirut to Bosnia' about Robert Fisk's reporting for the 'Independent' in the Muslim world.