There are people who say they are 100 percent sure we go to heaven, or are reincarnated, etc. and others that say they are 100 percent sure that when you die that is it. Face to face I take people at their word and of course I believe that at the time they said it, they were feeling 100 percent sure about their belief. Maybe it is just that I assume others think the way I do but I find it difficult to believe people are 100 percent sure, all of the time, about whether there is, or isn't an after life. I do think that people want to have more control over their lives than they are able to have. Maybe this is part of the equation concerning whether we believe or not. It is a way to calm our need to have certainty in our lives...
As long as we are alive things can change, all sorts of things, both good and bad: our beliefs, financial situation, friends, etc. Nothing in our lives is completely static. It is nice when you feel hopeful in a way that makes you look forward to future possibilities.