Final answer:
The main criterion that determines whether an action is unskillful often revolves around the action's intention and consequences. In many ethical systems, unskillful actions are those rooted in negative intentions such as greed or hatred and often lead to harmful outcomes.
Step-by-step explanation:
The main criteria that deciphers whether or not an action is unskillful can be quite complex and context-dependent. However, in many ethical and philosophical systems, such as Buddhism, an action is generally considered unskillful if it is rooted in harmful intentions like greed, hatred, or delusion. These actions typically lead to negative consequences for oneself and others. Conversely, actions that arise from compassionate, generous, and wise intentions are seen as skillful because they contribute to well-being and happiness.
In a broader context, whether in philosophy, psychology, or areas of personal development, an action might be viewed as unskillful if it does not achieve its intended outcome or if it leads to a negative impact on oneself or society. Therefore, the determination of skillfulness could be influenced by the motives, methods, and effects of one's actions.