Stoicism teaches the development of self-control and fortitude as a means of overcoming destructive emotions; the philosophy holds that becoming a clear and unbiased thinker allows one to understand the universal reason (logos). A primary aspect of Stoicism involves improving the individual’s ethical and moral well-being: "Virtue consists in a will which is in agreement with Nature." This principle also applies to the realm of interpersonal relationships; "to be free from anger, envy, and jealousy", and to accept even slaves as "equals of other men, because all alike are sons of God."
The word 'stoic' has come to mean 'unemotional' or indifferent to pain, because Stoic ethics taught freedom from 'passion' by following 'reason.' The Stoics did not seek to extinguish emotions, rather they sought to transform them by a resolute 'askēsis' which enables a person to develop clear judgment and inner calm. Logic, reflection, and concentration were the methods of such self-discipline.
'Follow where reason leads'.
The four cardinal virtues of the Stoic philosophy are wisdom (Sophia), courage (Andreia), justice (Dikaiosyne), and temperance (Sophrosyne), a classification derived from the teachings of Plato.
If someone is unkind, it is because they are unaware of their own universal reason which would lead to the conclusion of kindness. If they are unhappy, it is because they have forgotten how nature actually functions — unhappiness is having one's unrealistic expectations of reality go unfulfilled.