Why do Mary-Kate and Ashley Olsen wear those too-big sunglasses everywhere they go? Well, they learned an important lesson about appropriate eyewear recently at Hollywood's Chateau Marmont.

The twins were sauntering through the dimly lit celeb hangout with their shades on when they walked right into jewelry designer, Lisa Salzer, a spy tells the New York Daily News. "They all apologized to each other and walked on," the source says, "but the Olsen girls clearly couldn't see a thing." Maybe they need eyeglasses instead of sunglasses...