Sam Rabin was born in 1910 in Lutsk, Poland, the youngest of six children, with four brothers and two sisters. His father was a successful contractor who built streets and sidewalks and operated a cement factory, even devising a six-cornered cement paving brick set with granite. The family was comparatively well off, and many of their Polish neighbors worked for them. Sam's mother died of cancer when he was ten, a loss he never forgot, as he had been the youngest and always close to her side. His father later remarried, and Sam recalled a stepmother who treated him kindly. He attended a yeshiva and public school before beginning work with his father at fifteen.

As a child of about five, Sam lived through the violence of the revolution, remembering his father shielding him with his coat as Cossacks attacked Jews, and the family's harrowing flight from Lutsk toward Kovel and across the German border. He served in the Polish army beginning around 1931, enduring hardship and antisemitism, and was active in the Zionist Chalutz movement, playing soccer and enjoying river excursions. He built his own home before marrying his first wife in 1935 after meeting her in Kovel, a courtship encouraged by a local rabbi. They had sons, and Sam devoted himself to work and family until the war shattered everything.

When war came in 1941, Sam was mobilized and sent to fight in the Russian army, where he was wounded near Kiev after only weeks in battle. He was then sent to the Ural region for forced labor, cutting trees and building tank factories, eventually working as a supply clerk for years under difficult and dangerous conditions. Returning to Poland in 1944, he discovered that his first wife and children had been killed, and that he had lost dozens of relatives in the Holocaust. He joined a Zionist kibbutz in Wroclaw, hoping to reach Israel, and delivering drinks to shops. There he met and married Regina, a survivor he found waiting alone with a little girl at a train station, and together they began a new life that would lead them to Dallas.