I'm sorry about your grandpa. Losing loved ones is hard, and the first time a person close to you dies is extra-difficult. And I guess no one's ever come up with a definitive answer to why everyone's time on earth is eventually cut short. But as far as I know, a lot of religions focus on the idea that a person's physical self may die, but that their soul, the essence of their being, is everlasting and lives on in the world. That's an idea that I find comforting.