For instance, we are told: “A child’s memory, his power of remembering, may be exerted too much or too little in his ninth or tenth year.” The clamor against over-exerting the memory can lead to the result of exerting it too little. We must always try to find the middle course. For instance, we may make too great demands on a nine or ten-year-old’s memory. The real consequences will not appear before the person in question has reached the age of thirty or forty, or perhaps still later. Then this person may develop rheumatism or diabetes. By overexerting a child’s memory at the wrong time — let us say between the ninth and tenth year — we cause during this youthful stage an exaggerated depositing of faulty metabolic products. These connections, lasting during a man’s entire earth-life, go generally unnoticed.
On the other hand, by exercising the memory too little — that is, by letting a child’s memory remain idle — we bring forth a tendency to all kinds of inflammations appearing in later years.
What is important to know is the following: that the bodily states of a certain life-period are the consequences of the soul and spirit states of another.
Source: Rudolf Steiner – GA 226 – Man’s Being, His Destiny and World-Evolution: Lecture VI – Kristiana, 21st May 1923