Is it the decor, the service, or the variety in the menu?
Berkeley has a little takeout-only restaurant called Top Dog. It’s a hole-in-the-wall joint near the college campus. They sell hot dogs freshly made on a grill. You can choose a few varieties of sausages, like Frankfurter, Kielbasa. Service is not particularly friendly. You help yourself with sauerkraut and other condiments. There is no place to sit.
This place is nothing fancy, but people–students and old-time residents–love it. There are lines at midnight on weekends. People savor the hot dogs, standing on the street, spilling ketchup and mustard on their shirts. Then they order seconds.
Why do people go back? Consistency.
When people know what to expect, and you meet that expectation, you create what people want. The quality has to be solid, but it doesn’t need to be fancy.
But it has to be consistent.