Proverbs 27:17 "As iron sharpens iron, so one man sharpens another."
This verse really has two different messages to give us.
1) We have the ability to sharpen each other. We can encourage one another. We can keep each other accountable. We can also admonish each other when we start moving away from the spiritual goals that we aspire to. When God gives us the ability to do something, we should really see it as a responsibility to do something. It is our responsibility to keep each other sharp.
2) If iron sharpens iron, then iron can dull iron as well. If two blades strike each other they will dull. Keep in mind: One of the best ways to stay sharp is to have a partner you can go to when you need encouragement, prayer, and help. Someone who you can help to stay accountable, and who can to keep you accountable as well.