In an 1883 letter to his patron Nadezhda von Meck, Tchaikovsky describes his deep admiration for Pushkin’s genius and that he would be proud and happy if his music captured 10% of the beauty contained in Eugene Onegin poem. He confesses that if Onegin music is warm and full of poetic feeling, it is because his own emotions were intensified by the beauty of the subject.
... Pyotr Tchaikovsky recalled Lavrovsky's suggestion. Suddenly, Eugene Onegin the opera became a captivating idea. He spent a sleepless night sketching the opera to Aleksandr Pushkin's text
Apparently, Modest Tchaikovsky, composer's brother, criticized Onegin for potentially lack of scenic effect and action. This annoyed Pyotr, but he didn't care. He was immersed in the opera, in love with Tatyana's image, and enchanted by Pushkin's verse.