Dichotomy of Eternity and Instance

What's there to choose between an instance and eternity -- an eternity can be gone in an instance just as an instance can be experienced to eternity. Can eternity be experienced physically? Someone once said "Imagine a housefly orbiting the galaxy at its normal speed and once in a million years, it brushes past a metallic ball the size of the Earth. By the time the fly's repeated contact the metallic ball polishes the ball to nothingness, eternity would have not even begun." But with all the appreciation of our lack of grasp on eternity, we fail to take notice of all that happens in a whisker of a mere instance around us. If we cannot fathom all that happens in an instance, how can we treat Instance with disregard when compared to its daunting sibling, the Eternity?