In John Updike's A & P, Updike does know something Sammy does not.
Sammy is very idealistic at the beginning of the story. When "Queenie" arrives, he is nineteen and sees only how impressive she is. He is an innocent. He admires everything about her, even the way she walks. (Updike's imagery is not only amazingly presented, but particularly effective because he describes Queenie while showing us a great deal about Sammy.)
...and then the third one...She was the queen. She kind of led them, the other two peeking around and making their shoulders round. She didn't look around, not this queen, she just walked straight on slowly, on those long white prima-donna legs...you got the idea...she was showing them how to do it, walk slow and hold yourself straight.
Sammy sees her as regal—"queen-like," as she walks down the aisles of the store. She is glorious—he and his co-worker are used to seeing mothers with children, of "pin curlers" and "varicose veins"—these mean nothing to Sammy in his innocent world . It is, however, these humorous details that foreshadow Sammy's awakening. This episode is probably the last innocent moment of his young life. Queenie is an idealistic vision as he and Stokesie stand almost drooling as the girls move through the store.
The truth that Updike alludes to here is that Queenie is a brief illusion of Sammy's youth—that things change very quickly and the dream world he is immersed in, acting like a knight paying homage to a princess, is fleeting.
Then everybody's luck begins to run out.
Whereby Sammy is seeing his manager's re-entry to the store as the end of the fun for the boys—and the freedom of the girls to move about the store unaccosted by "rules"—it really foreshadowing that lets us know that everything is going to change—we just don't know until the end that the change is coming to Sammy. The girls are corrected by Lengel for the way they are dressed.
After the girls have been "put in their place" by the store manager—the world of the adult establishment has reared its ugly (but impossible to ignore) head, the "house of cards" starts to quiver as Sammy takes a stand:
"Did you say something, Sammy?"
"I said I quit."
"I thought you did."
[The knight defends his lady...]
"You didn't have to embarrass them."
"It was they who were embarrassing us."
This last line is really the crux of the entire story...the viewpoint of the "collective," that something as innocent to Sammy as bathing suits in a food store should be a "federal case." Perhaps because so much time has passed since this story was written, it's hard to understand why it was such a big deal to Lengel. However, if we put ourselves into the context of that moment, in that time, it was the way of the world.
"I don't think you know what you're saying," Lengel said.
"I know you don't...But I do."
Lengel tell him Sammy doesn't want to do this. Inside, Sammy agrees, but he notes:
But it seems to me that once you begin a gesture it's fatal not to go through with it.
As he leaves...
"I look for my girls, but they're gone..."
...my stomach kind of fell as I felt how hard the world was going to be to me hereafter.
Sammy has crossed an invisible line, standing up to the rules of the world. He isn't sure what it means, but Updike, perhaps one who remembers his own crossing of the line, does. There is a painful poignancy for all who remember life before, and life after, the crossing of the line—knowing how the world works.