To my understanding a steel does not sharpen a knife. A whetstone sharpens a knife by putting a smooth edge on the blade. This is good for a straight in cutting motion like a plane and not always good for a knife. A steel in fact roughs up the smooth sharp edge of the knife producing small serrations on the edge much like small teeth on a hand saw. Since most knives are used with a sawing motion these teeth cut better than a smooth cutting edge. None of you would try to cut through a piece of wood using the spine of your hand saw. A sharp smooth edged knife will cut nicely but the fine serrations will make it cut better