“Iron sharpens iron, and one man sharpens another.” Prov 27:17
Sharpening implies friction. To sharpen something, one must scrape the edge. Sliding the flat sides of pieces of iron together do not sharpen them. Talking with someone who always agrees with you does not sharpen you. But engaging with others about things we do not know, or about issues upon which we disagree, is challenging and forces us to grow and change. When we wrestle with others in this way, we become sharper, and therefore more effective. So it is important to resist the human tendency to avoid such friction because of pride and laziness.