Why does Jerry's mother feel she is too protective?

Jerry's mother worries that she is too protective because she feels that she may be causing her son to feel obligated to be with her, a condition which can lead to his loss of independence.
As a widow, Jerry's mother has a close relationship with him. In this story, she and Jerry are on holiday on the coast of a foreign country, and Jerry accompanies his mother to the beach each day. Anxious that she might be smothering the eleven-year-old boy's growing sense of independence, she asks Jerry if he would like to go somewhere other than their usual spot. Jerry tells her that he would like to "have a look at those rocks" which are in the distance. Although anxious about such "a wild-looking place," the mother gives her permission. Afterwards, she reassures herself silently that Jerry is an excellent swimmer. "She was determined to be neither possessive nor lacking in devotion"; however, it is not without anxiety that she goes to her beach.
Jerry's mother's faith in him allows the boy the opportunity to become independent later. At the "wild" beach he encounters older boys who can dive and swim through a rock tunnel under the sea. At first, they are somewhat friendly, but, after they realize he cannot perform this feat, the older boys reject Jerry. As a result, he secretly practices holding his breath and swimming underwater until he makes his "rite of passage" and successfully swims all the way through the tunnel.
Because of his understanding and unselfish mother, Jerry has completed a stage of maturation. After this, Jerry returns home. His mother notices that he looks pale and has bumped his head, but she does not question him further. When Jerry tells her he can hold his breath underwater for two or three minutes, she calmly responds,

Can you, darling? . . . Well, I shouldn't overdo it. I don't think you ought to swim any more today.

She does not need to say these things because Jerry feels that it is no longer important for him to go to the wild bay.