“arrogant heart.” See commentary on Proverbs 28:25.
“the lamp of the wicked.” The Hebrew literally reads, “the lamp of the wicked,” and the verse reads “Haughty eyes, and a proud heart—the lamp of the wicked—is sin.” However, that is sufficiently unclear in English to call for the addition of the italics to bring out more clearly the meaning of the verse: “the lamp that guides the wicked.” The genitive phrase is a genitive of relation, and in the biblical culture people used lamps so they could see and be guided in what they did, so the “lamp of the wicked” can be understood to mean the “lamp that guides the wicked.” The point is that, for the wicked, it is their own haughty eyes and proud heart that provides the light that they walk by, not the Word of God or the truth. Thus the proverb is saying that just as a person uses a lamp in a dark room to guide himself, the wicked are guided in what they do by their proud hearts and haughty eyes. But their proud hearts and haughty eyes do not perceive life as it really is, and they are sin in the eyes of God.
This verse explains why wicked people so often misread other people’s motivations and/or don’t get facts correct. They cannot see the world by the light of truth, instead they see the world by the light of their own arrogance and pride. When dealing with a proud and arrogant person do not expect them to understand or correctly assess your motives or actions; evil people will see evil in you even though it is not there, but you will usually not be able to convince them of that.