Terror, be sure of that, is not a bad ingredient of love. A man who wills fiercely to win the heart of a weak and vapourish woman MUST succeed, if he have opportunity enough.
 William Makepeace Thackeray, The Luck of Barry Lyndon (1844). copy citation

Context

“As I poured words to this effect out on the astonished widow, I stood over her, and fascinated her with the glance of my eye; saw her turn red and pale with fear and wonder; saw that my praise of her charms and the exposition of my passion were not unwelcome to her, and witnessed with triumphant composure the mastery I was gaining over her. Terror, be sure of that, is not a bad ingredient of love. A man who wills fiercely to win the heart of a weak and vapourish woman MUST succeed, if he have opportunity enough. ‘Terrible man!’ said Lady Lyndon, shrinking from me as soon as I had done speaking (indeed, I was at a loss for words, and thinking of another speech to make to her) —‘terrible man! leave me.’
I saw that I had made an impression on her, from those very words.” source