One who is full of good-nature will not insist on anything or get upset or angry about anything, nor be critical or disappointed about anything in the world. There is no character-trait better than this and it is considered a gift of Hashem.
Nevertheless, even one whose nature is bad can turn it over and change it by continuous profound reflection over pure thoughts, and by strengthening himself to remove anger and pain from his heart and to remove badness from his flesh, and knowledge for and understanding man makes it easy.
When a person will concentrate his attention to reflect with a correct and settled thought to seek the truth and to keep far away from all of the bad and forbidden character-traits, he will very soon open his eyes, see the despicability of the bad character-traits for they are all emptiness and badness of spirit. However, this is the evil of a person in the land, that he strengthens himself with his thoughts and draws himself out to seek claims and to give basis to falsehood until at the end it appears to him that he is correct and that his way is the right one.