Four types of people

Category 1: They know what they know. (These are excellent people because they can effectively use their ability in their respective field). 

Category 2: They know what they don't know. (These are good people because they will develop themselves).

Category 3: They don't know what they know. (These are bad people because they can never use their abilities)

Category 4: They don't know what they don't know. (These are worst people because they can never develop themselves. They always feel pride in spite of their inability.)