To be honest, after a little thinking about this, surely in this instance your very perception of the world around you borders on your optimism (in order to lend itself to "hope"). Delusional or not (take the desert island example that Mikus mentioned) it's your own self-belief and "hoping" that determines your take/perspective of how you live your life, irrespective of whether you're going to die in 3 hours or attempt to stay alive for as long as possible...
It's not the
chances we
take, it's the
choices we
make that I feel determines our destinies; they shape us and makes us individuals who react differently according to a plethora of reasons. If you opted to live a life of ignorant bliss, how would you be aware of the truth even if it
did occur? Equally, trying to "live" a life where you know what's going to happen (taking the stance that you can't change anything, otherwise we get into the whole changing destiny argument :p) brings both serious extremes of happiness and sadness. Thus, I can't help but feel that we need a little of both in our lives (if nothing else, just to keep us sane [or as close to it as some of us are going to get...] ;)) - we [mankind] ideally need "hope" to at least inspire us to continue and persevere

- regardless of wherever there may be some truth in some lies, or some lies in some truths...
Just a couple of my pondering there, exposed for all the net to see...
-Jackpot
On a (somewhat tenuous) semi-related note, the character "Caliban" from Shakespeare's "The Tempest" is an excellent example of the "nature vs nurture" argument....