Can friendship turn to into a a relationship?

I believe that a friendship  between a girl and a guy can turn into a really nice relationship. I cant say that it will always work, but i think that if they had a really nice friendship and they understand each other things can work out between them. But if you think about it sometimes one of the other don't feel the same for each other all the time, and at times i think that can mess up the friendship. I understand that sometimes they don't feel the same way when it comes to being together as a couple,but why mess up such a good friendship cause one is feeling the other more then the other. If they are really friends i think they would get through it. I believe that going through that can show you if they actually do care for you as much as they say. That's a really hard situation and i think that it mess up friendships but i believe that it shouldn't because real friendship doesn't die just like that.But i have always wonder if is really true that they aren't really feeling each other? or is it cause they don't  want to mess up such a good friendship? i honestly will never understand what goes through some peoples heads, because to me the best thing to do is be with your best guy friend, who better then that? they understand you they know most things about you and they still care and love you, i understand that not everyone sees things this way but it doesn't hurt to try. At the end of the day if it doesn't work out they didn't stay wondering if it would and they really were best friends they still be in each others life.