The phrase "to sharpen iron" means to improve or strengthen oneself or others through challenging or difficult experiences or interactions. Full definition
Its a well known saying that Iron Sharpens Iron so if its some professional issue or some work that's bothering you, try harder. (colossalcloset.in)
The advantage of a team made up of two very different perspectives is that a more balanced view is usually reached in the end — but the process of iron sharpening iron on a daily basis is usually not at all enjoyable, as spouses strive to change each other into a version of themselves. (familydisputesolutions.com)
You should be grateful as criticism from your opponents will sharpen your side's arguments for god — as iron sharpens iron. (religion.blogs.cnn.com)