One question I'm frequently asked is about knife steel rods or ceramic rods.
What do they do?
They are not actually for sharpening a knife like a stone, grinder or belt. What they do do is straighten the thin edge that gets bent from cutting. The stroking on the rod restores fine cutting by straightening the edge.
This only takes 1-2 light strokes on each side usually. Doing it more than that can just wear and break the thin edge and dull the knife.
If you are having trouble cutting a tomato skin run the knife (assuming it was sharp to begin with) on each side of a steel/ceramic rod and try the tomato again. Works great!