People who are good at self-examination know themselves well. That means they take a good, hard look at themselves. I call this "contemplating the self', meaning freeing one's mind and trying to reconsider oneself from the outside. People who can do this are able to understand themselves with humility and fairness.
Such people make few mistakes. I believe that this is because they are naturally unconstrained in discovering how strong they are, how much they can do, what their aptitudes are and where their weaknesses lie.
Source : "Sonokokoroikiyayoshi (That's the Spirit!)"