Some enchanted evening, you may see a stranger, and instantly you "know" that he is "the one." Then, once you've moved heaven and earth to establish the relationship that you just knew would make your life complete, you should fall out of love just as quickly and just as pointlessly as you fell in love. Nothing says, "emotionally stable" and "ready for a long-term commitment" quite like that.
(Cynical? Moi? What gave anyone that idea?)