From Kenopanishad

"vijnaatam avijaanatam avijnaatam vijaanataam"
This is from Kenopanishad.
The literal translation would be : "One who knows, doesn't know; One who doesn't know, knows"
Briefly, it would mean : The person who thinks, he knows completely about the Lord, does not know anything; and the person who knows that Lord cannot be known completely, knows about Him.
I have tried to translate and put across the points from Bannanje Govindacharya's book, 'talavakaarOpanishad'
According to the book, God cannot be known completely by anybody. If somebody thinks, he knows, then it is foolish. But, the person, who knows that one cannot know Lord completely, knows the truth; he at least knows that Lord cannot be known !
Vandana to Acharya