Tradition
St. Augustine
The Enarrations, or Expositions, on the Psalms
Psalm 64 › Section 10
10. But what befell them? “They failed searching searchings.” Whence? Because he says, “Who shall see them?” that is, that no one saw them. This they were saying, this among themselves they thought, that no one saw them. See what befalls an evil soul: it departs from the light of truth, and because itself sees not God, it thinks that itself is not seen by God....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)