As the story "A&P" closes, Sammy thinks "how hard the world was going to be him hereafter." Will it? Why? or Why not?
Yes, it probably will be hard for Sammy. He has reached a point of maturity from which there is no turning back. His world inside the supermarket was dull but safe. He has made a decision that will anger his parents and which will probably mean the end of their support, both financially, emotionally, and in the sense of being cared for like a child.
Sammy knows this as he makes his exit through the electric doors and into his life as a man. Sammy says, "I just saunter into the electric eye in my white shirt that my mother ironed the night before, and outside the sunshine is skating around on the asphalt."
The girls, of course, are gone, never knowing the grand sacrifice Sammy has made in their honor. He looks back, but sees that his absence has already been filled, his place in the store-society forgotten, like the tide filling in holes in the sand: "I could see Lengel," Sammy says, "in my place in the slot, checking the sheep through."
It's not a bad decision, he knows. Sammy looks at Lengel as he himself must have appeared to the outsiders, "(h)is face was dark gray." Still, knowing he cannot go back is difficult, for as anyone who has ever made an ultimatum knows, the future is uncertain. It's never easy to grow up.