Pain - Is it good or bad?

One thing my father said when I was growing up was Pain lets you know you're still alive. It was not a very positive thing to say when you're 7 but it wasn't untrue. But so many other times people are unable to answer my questions about pain. Is this pain a good pain? Does it mean whatever I'm doing is healing the problem? Does it mean stop whatever you're doing right now? Stop cause you're doing damage? Is the pain a result of an old injury that's still healing or a new one that I should be seeing a doctor about? Does anyone have the answers?