Solomon once declared in Proverbs 27:17 - "As iron sharpens iron [when they are rubbed together, of course, -SRB], so a man sharpens the countenance of his friend." It doesn't take long to dull a knife if you overuse it and abuse it. We too can become dull if we don't take advantage of opportunities to sharpen our mind and character in close association with godly friends.
However, it must be understood that close associations with others will not automatically result in sharpening ourselves in the Master's service. It all depends upon what you and your friends are made of. Are you made of iron or something even better, like steel? What about your close associates? If you are steel and your friend is lead, there will be no sharpening (and vice versa). When two pieces of iron or steel are able to rub together and sharpen one another, the result is a very rich and blessed experience. Nevertheless, if one material is corrupt or inferior, no sharpening will occur.
The apostle Paul taught that evil companions corrupt good morals (I Cor. 15:33). But, is this always and automatically true? I think the answer is no, but let me explain. Paul spent much time in the company of evil men (e.g., his persecutors who would whip him, throw him into prison, stone him, and eventually take his life). Why didn't evil company corrupt Paul's good behavior? Evidently, it was because he was stronger in goodness than they were in wickedness. He would not be subdued or distracted from his goal.
It is impossible that all of our associates in this world will be people of the highest character. We should choose our friends wisely, of course, and make the best of associations that are not ideal but must be endured (e.g., co-workers, neighbors, etc.). If you are blessed with a godly friend, you will endeavor to sharpen him as he is sharpening you. If you must regularly deal with a wicked man, whether he corrupts your good behavior or not will depend upon your strength. It is my prayer that you will be able to not only resist evil influences but overcome them with good, as Paul did with many whom he turned to the Lord (cf. Phil. 1:13; 4:22).