The basis of ones ethics will inform any downstream additions to their ethics, which in turn affect the decisions that person will make in their life. If someone has an ethical framework that is built on an inconsistent set of principles, their decision making will be rife with flawed reasoning, and will lead to irrational and illogical actions.
This is of course an inherently true assessment. If someone, for example, is taught an incorrect method to do basic math such as addition, it would be no surprise if they answered 2+2 by shouting “5!” Someone who has been taughta poor set of ethical first principles will of course act ultimately in an unethical matter, even in spite of potentially holding “good” higher values. This is especially seen in the religious context; Christians and Muslims will pat themselves on the back for investing faith in a beautiful religion, and yet commit gleefully some of the most heinous and barberous acts. This is not to single out Christians or Muslims, anyone is capable acting out great evil so long as their first ethical principles are inherently twisted.
The Philosopher (Aristotle) posits in virtue ethics that it is the responsibility of the individual to seek out and adhere to good ethical principles. While Aristotle lists himeself a fine set of principles, he implicitly states, rather than explicitly, that very foundational ideal of holding true to good first principles above all else. Man may be corruptible, but holding incorruptible ideals brings us that much closer to godliness.
But what are good ethical principles? As stated previous, any principle that has an inherent logic fallacy to it cannot be a good principle. Having exceptions, rather than absolutes, also allows for evil, or even just plain human negligence, weakens the strength of the principle. Finally, good foundational principles cannot be based on destroying others, or the self. This is the most important facet of first principles because to destroy the self is todestroy humanity. If the principle is based on destroying the self, it drives the man to the level of the animal; it transforms the man into an object to be used either by his base animalistic instincts, or to be formed into a servant of other men. Principles exist to service, and better the self, and never destroy the self. The destructions of others also cannot be tolerated, as any principle that requires the destruction of others, in turn, allows others to destroy that man. In this version of Game Theory, the Nash Equilibrium leads to the destruction of both parties. As such, the primary first principle must always be based on The Golden Rule: Treat Others How One Wants To Be Treated. If viewed through the Rawlsian Veil of Ignorance, any world in which everyone is treat how they want to be treated, would result in a calm, peaceful world, as no one wants to be abused or hurt by others.