Buddhist ethics have come to be known as psychological only for this reason. The innermost depths of human personality are measured and the forces molding the thoughts and attitudes are laid bare by Buddhism so that moral behaviour could be mastered and perfected. Knowledge and will are the twin sides of the same coin. False knowledge and perverse will are the sources of pain and suffering. Mind must be trained both in the matter of intuiting the truth and of the conquering the passions.
Impermanence is built into the very structure of the world.
Change is the very stuff of reality. Nothing is an exception to this law. Holding onto things under the delusion that things will endure causes suffering when they pass away in spite of one's best wishes and efforts. Right knowledge and belief in impermanence save us from the delusion of permanence and consequent despair. One direct consequence of such a knowledge is the practical outlook of compassion and tolerance.