All knives gradually dull due to use, keep them in tip-top condition by using a sharpening steel regularly. A few strokes of both sides of the knife over the sharpening steel will help you to maintain the sharpness of a good blade. 

A traditional butchers steel like this Wusthof steel will maintain an edge, we recommend also using a Diamond Steel or a Ceramic Steel to restore the sharpness of particularly blunt knives.