If you expect to die, things like crossing the street, eating unhealthy food, doing drugs, etc., are just going to affect the timing. But if you think there's a chance you won't die, you can think of these things as slightly killing yourself, instead of changing the date of your death. So it makes you more conservative.
But it also makes you more optimistic! Someone who admits to maybe living for a very long time will probably want to invest a lot in having multiple possible careers, not to mention lots of money saved up. This basically amounts to maximizing positive surprises (you can take advantage of more career and investment opportunities) and minimizing negative surprises (losing a job when you have a month's worth of savings is a crisis -- losing your job when you've saved forty years of expenses is a blip).
In the movie "Big Fish" by Tim Burton, an excellent film about father-son relationships, there is a scene where the son goes to an oracle and learns how he is going to die. After learning how he is going to die, he takes on various death-defying stunts without consequence - for he knew that was not the way he was going to go.
