The big question

So where does one start when trying to choose principals that determine right and wrong? It is such a big thought to think that one person could understand what is truly always right and always wrong. We are also prone to favoritism. Wanting to make exceptions for some of our favorite activities that even in passing consideration are clearly wrong. Or exceptions for loved ones, or those who don't "understand." Part of the difficulty is that weather we know it or not, we always start with our own experience.