A man is definitely known by the company he keeps. Company goes a long way in influencing you. One is supposed to learn from others in our vicinity, but the one can pick up good things and even bad things. At times, your friends inspire you, console you when you are down and act as your support in adverse circumstances. But, friends who indulge in all sorts of wrong doings, addiction etc. will influence you in a wrong way. You might end up picking their bad habits.
As George Herbert has put forth, "Keep good men company and you shall be of the number. Keep not ill company, lest you shall increase their number". So, be wise when it comes to choosing a company. Company of the right person is extremely vital for your benefit and progress. The right friends always shield you from negative vibes and influences, acting as your alter ego.