This singular fact is due to the following circumstance: when animus and anima meet, the animus draws his sword of power and the anima ejects her poison of illusion and seduction. The outcome need not always be negative, since the two are equally likely to fall in love (a special instance of love at first sight).
The language of love is of astonishing uniformity, using the well-worn formulas with the utmost devotion and fidelity, so that once again the two partners find themselves in a banal collective situation. Yet they live in the illusion that they are related to one another in a most individual way. ~Carl Jung; The Syzygy: Anima and Animus Aion (1951). CW 9, Part II: P.338.30