"You canker blossom!" 3 Shakespearean Insults
c.1200, innsihht, "sight with the eyes of the mind," mental vision, understanding," from in + sight. Sense shaded into "penetrating understanding into character or hidden nature" (1580s).
insight in·sight (ĭn'sīt')n. Understanding, especially an understanding of the motives and reasons behind one's actions.