Even if it is fate, why was Regina not suspicious that 18 years pass before suddenly Gold has a baby? Adoption can take awhile but 18 years? Perhaps she was really picky –has to be a baby, boy, brown hair etc. I could see her giving Gold a list of demands.
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“If I had a world of my own, everything would be nonsense. Nothing would be what it is, because everything would be what it isn't. And contrary wise, what is, it wouldn't be. And what it wouldn't be, it would. You see?” -- Lewis Carroll, Alice's Adventures in Wonderland & Through the Looking-Glass