Why are fast casual restaurants like Shake Shack doing so well?

The burger chain Shake Shack told investors on Monday that it plans to expand aggressively in the years ahead. Its goal is to eventually operate 1,500 stores. Currently, it has just over 300.

The move comes as the fast casual segment of the restaurant business is growing much quicker than other parts of the industry.

There’s no Shake Shack where I live (yet), but Jersey Mike’s just opened its second location in the area. So I went for lunch. It’s next door to a new Dave’s Hot...