Why can't I comfort people?

I don't know what my problem is. When my grandmother died my sister was deeply affected. I just didn't know what to tell her. I was sad to but... in a quiet way. Usually I'm really good with words. Friends and family come to me with advice, and I feel I do right by them. But when it comes to death, I just don't know what to say. Is it my own feelings about death that keep me from being a comfort to those in need? I just see it as a natural part of life. I mean sure it's sad, but... what can you do? No amount of grief is going to bring them back. How do you comfort someone when someone they loved has passed?