What is the deal with poeple advising you to spend time with positive people..?

Everywhere i see people suggesting you to spend time with positive people, saying it'll rub off on you.. So what do I do, just leave all the negative people who are close to me? to deal with their own issues, stop empathizing with them? to hell with everyone?? Plus how can you relate to someone who is always so positive when you yourself are not..