On living forever...

Bumped into someone today whose mum is fairly ill. Noticing that a parent (or I suppose a close friend) is failing comes as a crushing reminder of our mortality. But why should we need reminding? After all the only things certain in life are "death and taxes". And yet, most of us spend most of our lives thinking we'll live forever. Or do we just not think about it? Seeing someone important approaching death makes the reality of the end of life difficult to avoid.