Never+before+that+night+had+I+felt+the+extent+of+my+own+powers+--of+my+sagacity

Never before that night had I felt the extent of my own powers --of my sagacityThe Tell-Tale Heart

This sentence is a great sentence. Sagacity- the quality of being [|sage], [|wise], or able to make good decisions synonyms: [|wisdom], [|sapience] So he is saying never before that night had I felt the extent of my own powers of my wisdom or ability to make good decisions.