Dating back hundreds of years, and extending into very recent times, some main-stream Western European values held that women may propose marriage only in a leap year.
Though the details are dubious at best, Ancient Irish legend recounts that the custom started in 5th century Ireland, as St. Brigid of Kildare argued that women were waiting far too long for men to propose marriage. St. Patrick, empathetic with this, declared that women could propose marriage to men, but only on this one, auspicious day. Of course, a nun and priest had to be the ones to figure all of this out - how ironic.