The thoughts invested in this work are the result of observations and experiences on the basis of feeling that have accumulated over the past five to six years. I was going to write a large book, for which it would be necessary to undertake a number of experiments in the field of feeling. But in view of other also important works, I had to abandon this plan, at least in the near future. Perhaps I will never be able to fulfill this task. Someone else will make it fuller and better, as there is a need for it. Thus, I have to limit myself to pointing out this major problem. I will consider myself happy if this instruction does not remain fruitless.