Light travels in a straight line.
Light will continue moving in the same direction unless it hits something.
Upon striking the surface of a lens, the path of light will change direction.
Though it is not exactly the same idea, it may help to think about the last time you were directly in front of a mirror. In this case, the light would have continued on in the same direction but it hit the surface of the mirror and was reflected back at you. With refraction we are looking for a much smaller change in direction in comparison to the aforementioned 180 degree turn.
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