Humans like certainty.
We like to think that we have all the information, that we understand things around us, that we're right about how we think the world works. We know that the earth's orbital period is 365.25 days. We know that atoms are composed of protons, electrons, and neutrons. We know that you can't dig a hole to China, that water boils at 373.2 kelvin, that crustaceans feel pain, and that chocolate melts in cookies to delicious effect.
We overwhelmingly want to feel like we have a firm grip on the whats, whys, and hows of everything from economics to environment to biology. This is both understandable and problematic.
I submit to you that life becomes a place of much more wonder and amazement if we recognize -- and allow ourselves to be awed by -- how much we don't yet know or understand about the space in which we exist. What inspires more hope, more fascination, more innovation and collaboration, than being able to say "Wow, look how much we have to learn!"
This is all just a big lead-in to say, read this:
Via NPR, the answer to life, the universe, and everything is 63.