I think it a fair comment to say that some text books on psychology are written on exactly the opposite assumption, namely that the ideas discussed by their authors (and other ideas which they have not yet thought of) will ultimately be able to describe adequately and accurately all human behaviour, and all human relationships. If this comment is correct, then in my opinion it is a classic mistake of the first magnitude, and simply is not true. If psychologists and psychiatrists do write like this, however, it is easy to see how they came to make the mistake: they inherited this attitude of mind from the physical sciences. In experimental physical science one has to make two basic assumptions, as Max Plank explained in his book “The Universe in the Light of Modern Physics”. Neither of these assumptions is capable of proof. They are just assumptions. The first assumption is that cause and effect is the rule over the whole of creation, which in experimental science is based, as David Hume has pointed out, on the logical fallacy of post hoc - propter hoc. If B follows A in everyone of 1000 experiments, we say A causes B. The second assumption is that there is in nature or creation a universal plan or plan of growth, which never contradicts itself.
The combination of these two unprovable assumptions is the idea that every event or action that happens in nature can, in theory, be analysed or explained. For practical reasons this idea was assumed to be true in the physical sciences until recently, although it seems debatable whether its validity does not break down when it comes to a consideration of the quantum mechanics and the statistical mechanics. However in the last twenty years, the prophets of the new science of Chaos or aperiodicity claim the first assumption is hopelessly wrong whenever you find there is a sensitive dependence on initial conditions. For instance, in the turbulent flow of fluids, of gasses as in the atmosphere, of liquids as in streams and rivers, generally the paths of particles are chaotic, and not ordered; although you can get areas, often…