Sunlight can be absorbed or reflected in several different directions. Sunlight that is bouncing off horizontal surfaces such as water, land or the hood of a car is usually reflected back in a similar horizontal direction. This reflection produces an agitating source of glare that cannot only create visual discomfort but can also cause a potentially blinding glare.
Glare has the potential to create a very dangerous situation. Polarized lenses contain a filter that allows only vertically oriented light to pass through and therefore blocking horizontal light and reducing glare to an absolute minimum.