In the short story "Through the Tunnel," what is the author suggesting about the process of maturation?

Doris Lessing, the author of "Through the Tunnel," seems to be suggesting that the process of maturation is not a linear one. As we grow up, we don't neatly proceed from one step to the next in an orderly fashion, eventually ending up at the goal after we've taken each step in order and only once. The process of maturing is a great deal messier than that; the path is twisted and winding, sometimes turning back on itself for a time.

To begin, Jerry seriously desires some independence from his watchful and protective mother, and he longs to go to the "wild bay" to begin to achieve this. When he eventually does get there, he comes across some "big boys -- men to Jerry," and his desire to be accepted as one of them, a man, overwhelms him. Later, however, rejected by them, he "cried openly, fists in his eyes" and "he cried himself out," as a child would.

He has realized that he needs goggles in order to attempt the feat that those boys did -- swimming through the tunnel in the rock -- and he assaults his mother, unable to delay gratification (the ability to do this signals maturity), "defiant and beseeching" because he needs them "now, now, now! He must have them this minute and no other time." This is very childlike behavior.

As he practices holding his breath, day after day, "that other beach [...] seemed a place for small children [...]. It was not his beach." Jerry is beginning to have a sense of the patience one must exhibit in order to achieve something substantial. When he decides to go to the wild bay that day, "He did not ask for permission [...]." Adults do not ask permission; children do. Moreover, although he now believes that he could probably make it through the tunnel, "A curious, most unchildlike persistence, a controlled impatience, made him wait." He is acquiring the ability to delay gratification, a sign of his growing maturity and waning childish impulsiveness.

However, in achieving his goal of swimming through the tunnel he had been extremely frightened by it, and "He could see the local boys diving and playing half a mile away. He did not want them" anymore. Fitting in with those "big boys" had once been his primary goal, but it no longer appeals to him. Jerry, perhaps, has realized that he is not quite ready to be a man yet. In the end, he calls his mother "Mummy," a quite childlike way to address her, and blurts out that he can stay underwater for three minutes now. "It came bursting out of him," like a child would speak when seeking his mother's approval. It is now no longer the boys' approval he desires; he doesn't need their recognition as a fellow man. He is content, for now, to remain a child and accept his mother's praise and instruction without a "battle of wills."

This back-and-forth movement -- desiring independence one minute, displaying an inability to delay gratification the next, using patience and level-headedness to make a mature decision, and then reverting to childish tendencies and behaviors -- shows that the process of maturing is not a straight path from point A to point B. Instead, in this process, we often take two steps forward and one step back.