Freud, who had called Fliess "the Kepler of biology", later concluded that a combination of a homoerotic attachment and the residue of his "specifically Jewish mysticism" lay behind his loyalty to his Jewish friend and his consequent over-estimation of both his theoretical and clinical work. Their friendship came to an acrimonious end with Fliess angry at Freud's unwillingness to endorse his general theory of sexual periodicity and accusing him of collusion in the plagiarism of his work. After Fliess failed to respond to Freud's offer of collaboration over publication of his "Three Essays on the Theory of Sexuality" in 1906, their relationship came to an end.