Curiosity really. Things will happen in the next 50 years that I'd like to learn/know/see/do, and something (life) is better than nothing (death). Even if I knew in that all the broader goals of my life I would fail and be miserable, I'd still derive some pleasure from reading and learning and just observing humanity as a whole. Allie Brosh wrote two excellent blogs about depression that you may enjoy (or at least relate to, my partner swore this was the best explanation for her depression): http://hyperboleandahalf.blogspot.com.au/2011/10/adventures-...http://hyperboleandahalf.blogspot.com.au/2013/05/depression-...