If the iron is dull, and if it was not that way before, but has been made dull by much labor, then it will be sharpened. And wisdom will follow after diligence
Other versions
King James Version
If the iron be blunt, and he do not whet the edge, then must he put to more strength: but wisdom is profitable to direct.English Standard Version
If the iron is blunt, and one does not sharpen the edge, he must use more strength, but wisdom helps one to succeed.New International Version
If the ax is dull and its edge unsharpened, more strength is needed but skill will bring success.