The Law of Limited Knowledge:
1. No matter how smart you are, there is always someone smarter.
It follows there is no way, through smartness, to make sure you are not being outsmarted.
2. No matter how sure people are they're right, they may still be wrong.
Certainty is a state of mind. It is, perhaps, a feeling or even an emotion. It is also an attitude. It involves a closing of the mind and can have a defiant aspect: "I know it! period!" Certainty has degrees, from absolutely certain to very uncertain. But the point here is that certainty is a state of mind and has nothing to do with the truth. A person can be absolutely sure of something that is false or very uncertain about something that is true. (The idea of Certainty States was developed in conversations with now Dr. Spencer Kagan, in informal discussions we had in our college days.)
(The opposite of the state of Certainty is the state of Uncertainty. Most do not like the feeling of being Uncertain. Most people do not like the feeling of being wrong.)
3. No matter how much you know, there is an infinite number of things you do not know. There is even an infinite number of things you don't know about any particular subject or object (or person — including yourself).
Another way to put this third point is that, no matter how much we know, (individually or collectively), the sum total of our knowledge is infinitely small compared to the sum total of possible knowledge.
It follows that no matter how sure you are that you are a good person, it is possible that you are not acting in an upright and honorable manner but out of a motive hidden to yourself.
4. To learn the Law of Limited Knowledge as it applies to yourself is generally an unpleasant thing to learn. However, it is a necessary step (an early step but one that has to be learned over and over) for those interested in learning about themselves.