We are still very much at the earliest stages of learning how a human being learns. So desite admonitions dating from anchient times, it is not clear if punishment or pain is required for child rearing. Evidence suggests that learning occurs when ones brain repeatedly receives multiple impulses from our senses. Coupled with suitable reward or other forms of what we think of as pleasure, connections in the form of new synapses grow between nerves in the brain. These provide electrical and chemical links so that a similar future nerve signal from one sense will conjure up memory of the related experiences.
Initially a newborn infant receives sensual experiences such as taste, warmth, and cuddling pressure which are associated with the positive nurturing process of being fed. Within the first few month of life an infant usually learns to associate the sounds of their mother's voice and the visual information of the mother's face (and those of other nurturing parents and individuals). Later development associates particular sounds including clues of language communication with the arrival of food and comfort.
In the early months after birth, an infant begins to learn that by crying they might influence aspects of their immediate future. (For example, crying to indicate hunger often brings feeding.) They learn that they have some control of their limbs and head and that certain nerve signals correlate with positions and actions of body parts. (For example, feeling motion of a finger is correlated with seeing that finger move. So later we can move a finger or bend a knee and know its location and how it moved even with eyes closed.) Gradually they learn that they can control the natural grasp of their hands and mouth and use those to occasionally control parts of their environment. (Shaking a rattle, positioning a nipple in ones mouth, and such.) The classic example of learning to suck one's thumb or hand is an example of an infant learning to control and coordinate several parts of their body.
Additional experiences build more extended but linked chains of associations. Some memory links are of very pleasant and nurturing experiences while others are of less satisfying events. The discomfort of hunger, the pain of intestinal gas, the exposure to cold and frightening experiences provide associations of activities or situations worth avoiding. Gradually an infant learns to differentiate and select actions which produce more desirable consequences and avoid those which produce less desirable consequences. (Smiling is generally reinforced while a great many other strange facial expressions fall into disuse.)
There is considerable evidence that a sparse environment retards a child's development. But evidence is also beginning to show the importance of that environment being controllable by the child. A television or hanging mobiles may attract ones attention, but a child needs to have experiences where they can manipulate and change what is nearby. A television might provide an immediate pacifier, but it fails to develop motor skills, coordination, and higher thought analysis processes. (As for adults, television may be interesting, but it rarely promotes development of many skills.)
Returning to the original tag-line, Spare the rod and spoil the child: It appears that punishment, pain and other undesirable consequences function by helping to learn what is NOT a desirable action. It doesn't directly teach what alternate action should be substituted. To avoid touching bare electrical wires or a hot object, a particular alternative is not important. But for most situations where a preferred action is desired, punishment may not be not very helpful.
A figurative meaning of using the rod may have more value: It is important to learn what is unacceptable. Any teaching situation which only uses positive reinforcement and reward may be deficient in being unable to teach what is unacceptable. (That is, there is an important distinction between situations which are unacceptable from those with neutral value.) Ideally the rod might be a simple verbal NO. But at times other means of communication can help desired learning. Actual physical restraint is appropriate in some situations. And in rare situations, brief pain may help bring attention to a matter of acute importance. That said, there seems little evidence that long-term punishment much helps learning. (While sometimes presumed identical, the loss of a privilege due to demonstrated inability to handle it appropriately is NOT the same as long-term punishment.)
Life on earth often involves hardship, sometimes pain and much that seems less than ideal. A child needs to learn to live within such an environment, both working in and coming to enjoy the situation provided. While there may be opportunities for improving ones lot in life, most of the time a person needs to find happiness and pleasure in what conditions are currently available. And those are nearly always less than what one might dream possible.
It is now common for many people to pacify themselves with television or internet entertainment. In past centuries it was more common to find hobbies or games of distraction. The ideal solution would seem to be for an individual to learn contentment, finding pleasure and satisfaction with the situation currently at hand. If that is so, then it is relevant to ask how is contentment learned, and how could that be taught?
But first consider what seems a deeper question: How does one learn to act out of love; how can one be taught to selflessly live one's life caring for the welfare and benefit others? In answering that may lie the solution to the previous questions.
Life on earth appears to have had but one origin, with more advanced life forms built on adaptations of what was successful earlier. On rare occasions a new mechanism was developed, but generally the previous mechanism continues to work. This is particularly apparent in the various systems for responding to changes in the environment. The most primitive of living creatures have nerve systems which are described as hardwired; When a stimulus is presented, the electrical signal directly causes muscles to contract. Similarly, some systems provide a chain of feedback mechanisms such that one action is always followed by the same sequence of actions. Another response system developed by both plants and animals utilizes chemicals such as hormones; this provides a way to have influence on multiple systems at diverse locations within an entire large organism but often responds much slower that alternatives. Humans still use such mechanisms, but these don't provide means for significant learning. Amoeba use a primitive hydraulic system for the motion; but only a few advanced creatures such as the starfish adopted it for multi-cell communication. (Although some individual cells such as leukocytes, white blood cells, continue using it.) But the system described above which provides for all the spectacularly varied behaviors of higher animals involves learning by forming connections between brain neurons. This actually involved two separate but related systems which provide short-term memory and long-term memory.
Nearly all that we usually refer to as learning involves the single mechanism which is described as long-term memory. (This is explained in more detail in Biochemistry 7: Memory.) While there are other mechanisms (described in the previous paragraph) used for responding to stimuli, long-term learning involves only one mechanism. So the challenge is to understand how this single mechanism involving formation of new synapse links between brain cells can seemingly have conflicting characteristics.
The key to understanding love is recognition that since it involves an unselfish action that benefits another person and not oneself, the action does not provide any direct reward or pleasure. As a result, it almost always involves at least some inconvenience, often some amount of discomfort and occasionally even pain. A superficial analysis would suggest such activity would be discouraged and avoided as typically is true with most activities which receive punishment. But since love involves the same mechanism which drives or motivates other actions by their chain of linkages related to reward, pleasure or nourishment, love must also be understood to somehow involve that same kind of reward mechanism.
This must lead directly to the hypothesis made in the essay What is Love? the pinnacle of Biochemistry! that love must be learned by association with earlier activities which did provide sufficient pleasure or reward to make the new action done selflessly seem worth of doing.
If that hypothesis is correct, then even very young infants may begin to learn how to act selflessly in Love. Just as new infants begin to learn patience, for example that they may need to tolerate being exposed to cooler air while diapers are being changed, they are also learning that experiencing such displeasure is associated to feeling comfort afterwards. That is exactly the same sort of association that, if consistently supported during childhood, should eventually empower that individual to Love. The key feature is that inconvenience, discomfort and perhaps occasionally even pain is associated closely and reliably in time with pleasurable experiences such as again being warm, comforted, and fed. So we have again returned to spare the rod, and spoil the child. Without some negative experiences, but those reliably coupled to pleasurable ones, an individual may not develop much capacity to Love and act selflessly. The notion that a child should ALWAYS have only positive experiences may actually create a handicap.
It should also be noted that the capacity to Love is also likely to be handicapped if a child lives in an environment without experiencing Love from others. If the pleasurable experiences of being warm, comfortable, and nourished are lacking, the individual may not learn by association the capacity to Love. So the adage may also be true, that for children to learn to love, they need to grow up in loving families.
And finally, contentment and the ability to tolerate and perhaps even enjoy ones current situation may simultaneously be learned by the same associations involved in teaching a person to love!
Before ending, it may again be appropriate to note that we are still very much at the earliest stages of learning how a human being learns. As in any new area of developing science, the understanding, hypotheses, and other proposals should be regarded as tentative and open for debate. Should further observation and experimentation provide supporting evidence, they can later be considered more certain. But especially in developing new understanding about human behavior and learning, one should remember there is significant risk of error. So one should utilize the above ideas with caution.