The sun’s rays shoot light in all directions, so when a sun ray hits a flat surface like water, the reflected light shines back at your eye and is magnified. Glare is like buzz killington and the bringdowns on your day. It reduces your depth perception, distorts your vision and color perception, and can even temporarily blind you. Not good or cool in any way.
Regular crappy sunglasses are designed to only reduce the light that is transmitted through the lens horizontally and vertically. But the chemical filter on the lens of a pair of polarized sunglasses is designed to absorb horizontal light waves, while also still allowing vertical waves to pass through it. Because the sun light only travels in one direction through polarized lenses, glare is completely eliminated.