Sam Il-Rumi came to the United States with his parents and brothers in 1980, fleeing the occupied West Bank and settling in New York, where his father opened a pet-food store in the East Village. Sam was a young man when he arrived, and within nine years he had acquired and sold two delis in the West Village and opened his own pet-supply store on Montague Street in Brooklyn Heights, where he has remained — the hardiest plant in the most unforgiving weather.

Montague Street, once the prime shopping artery of an affluent neighborhood, has few of the sort of independent stores that people who live near it actually want. Like so many other commercial stretches of the city, it has storefronts that have been vacant for months and even years. When Sam first established himself in Brooklyn Heights, Yemeni immigrants owned many of the businesses. The narrative that followed featured the predictable story arc: Rents went up and up and up; Amazon and FreshDirect colonized our shopping habits; cellphone stores and urgent-care facilities descended.

Though a few years ago he had to let workers go, Sam has persevered. At any given point in his seven-day workweek, he can be found in his store alone, or outside greeting people, familiar with everyone and everything — every cocker spaniel and Maltese, husband and wife, wet-food preference, dry-food preference. Not long ago, he introduced a customer who was widowed to another regular; the two decided to marry. Over the decades that Sam developed this devoted following, he became a homeowner and raised five children — one of them now works in marketing, another is now in dental school.

The likelihood of a scenario like that unfolding today seems fairly slim. For the millions of immigrants who came to this country during the 20th century, entry into the merchant class was a viable and important path to prosperity. A new exhibit at the Tenement Museum on the Lower East Side — “Immigrants Mean Business: An Enduring History of Entrepreneurship” — reminds us of the outfits that began in pushcarts, grew to institutions and spanned generations. Today, there are 83,000 businesses in New York owned by people who came to the city from another country.