With each use of your knife, the edge naturally bends over just a microscopic bit. The edge is still sharp, but the sharpest part isn't making contact with the food. The remedy for this is honing. Regular honing realigns the edge so that sharpest part contacts the food, enabling you to go longer between sharpenings. While fine European knives can require honing after each use, Shun's harder steel means you can hone just once a week or so, depending on your level of use.